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Logistic Models (logistic + models)
Selected AbstractsA re-examination of distance as a proxy for severity of illness and the implications for differences in utilization by race/ethnicity ,,HEALTH ECONOMICS, Issue 7 2007Jayasree Basu Abstract The study analyzes the hospitalization patterns of elderly residents to examine whether the relation between distant travel and severity of illness is uniform across racial/ethnic subgroups. A hypothesis is made that severity thresholds could be higher for minorities than whites. Hospital discharge data from the Healthcare Cost and Utilization Project (HCUP-SID) of the Agency for Health Care Research and Quality for New York residents is used, with a link to the Area Resource File and American Hospital Association's survey files. Logistic models compare the association of distant admission with severity corresponding to each local threshold level, race, and type of hospital admission. The study uses four discrete distance thresholds in contrast to recent work. Also, an examination of severity thresholds for distant travel for different types of admission may clarify different sources of disparities in health care utilization. The findings indicate that minorities are likely to have higher severity thresholds than whites in seeking distant hospital care, although these conclusions depend on the type of condition. The study results imply that if costly elective services were regionalized to get the advantages of high volume for both cost and quality of care, some extra effort at outreach may be desirable to reduce disparities in appropriate care. Published in 2006 by John Wiley & Sons, Ltd. [source] Groundnut consumption frequency in GhanaINTERNATIONAL JOURNAL OF CONSUMER STUDIES, Issue 6 2008Curtis M. Jolly Abstract Groundnut (peanut) is an important food and oil crop in Ghana, but little is known about the factors influencing consumption. The study surveyed market participants; investigated the frequency and forms of groundnut consumed; and evaluated the factors influencing consumers' decisions to eat groundnuts in Ghana. About 80% of respondents consume groundnut and/or its products at least once a week and 32.0% consume it three times a week. Logistic models showed that age, education and the form in which groundnuts are consumed influence the frequency of groundnut consumption. Total revenue and the form in which groundnut is eaten influence farmers consumption decision whereas groundnut consumption by poultry farmers is influenced by knowledge of the health effects of groundnuts on birds and the form in which groundnut is eaten by the poultry producers. Processors' frequency of consumption is influenced by the form in which groundnut is consumed and their knowledge of reasons for sorting. The results are important for market segmentation for demand projection along the marketing chain. [source] Hospice Usage by Minorities in the Last Year of Life: Results from the National Mortality Followback SurveyJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 7 2003K. Allen Greiner MD OBJECTIVES: To examine racial/ethnic variations in rates of hospice use in a national cohort and to identify individual characteristics associated with hospice use. DESIGN: Secondary analysis of the 1993 National Mortality Followback Survey (NMFS), a nationally obtained sample using death certificates and interviews with relatives (proxy respondents) to provide mortality, social, and economic data and information about healthcare utilization in the last year of life for 23,000 deceased individuals. SETTING: Hospice care. PARTICIPANTS: Individuals aged 15 and older who died in 1993. Subjects were included in this analysis if they died of nontraumatic causes (N = 11,291). MEASUREMENTS: Hospice use was dichotomized by proxy responses indicating use or nonuse of home or inpatient hospice services. The percentage of individuals using hospice services in the last year of life was calculated. RESULTS: Unadjusted bivariate results found that African Americans were less likely to use hospice than whites (odds ratio (OR) = 0.59; P < .001) and that those without a living will (LW) (OR = 0.23; P < .001) and without a cancer diagnosis (OR = 0.28; P < .001) were less likely to use hospice. The negative relationship between African Americans and hospice use was unaffected when controlled for sex, education, marital status, existence of a LW, income, and access to health care. Logistic models revealed that presence of a LW diminished the negative relationship between African Americans and hospice use, but the latter remained significant (OR = 0.83; P = .033). A subanalysis of subjects aged 55 and older showed a significant interaction between access to care and race/ethnicity with respect to hospice use (P = .044). Inclusion of income in this multivariable logistic model attenuated the relationship between African-American race/ethnicity and hospice use (OR = 0.77), and the difference between whites and African Americans became only marginally statistically significant (P = .060). CONCLUSION: In the 1993 NMFS, hospice use was negatively associated with African-American race/ethnicity independent of income and access to healthcare. The relationship is not independent of age, insurance type, or history of stroke. For subjects aged 55 and older, access to healthcare may be an important confounder of the negative relationship between African-American race/ethnicity and hospice use. Consistent with previous studies, this analysis found that African Americans were less likely to use LWs than whites. The reduced importance of African-American race/ethnicity on hospice use with the inclusion of presence of a LW in logistic models suggests that similar cultural processes may shape differences between African Americans and whites in advance care planning and hospice use. [source] Alcohol and Atherosclerotic Vascular Disease Risk Factors in French Men: Relationships Are Linear, J-Shaped, and U-ShapedALCOHOLISM, Issue 1 2005Philippe Rouillier Background: Although it is well admitted that alcohol displays a U-shaped relationship with atherosclerotic vascular disease, individual relationships between alcohol and atherosclerosis risk factors may be different and have not been determined precisely for several of them. Methods: A cross-sectional study within the SU.VI.MAX French cohort study was performed to assess the curve of potential relationships between alcohol and atherosclerosis risk factors in 2126 healthy men. Mean daily alcohol intake was derived from 37 alcoholic beverages in twelve 24-hr dietary recalls. Logistic models were adjusted for age. Results: Apolipoprotein B (ApoB), fasting glucose, body mass index, waist-to-hip ratio, and waist circumference displayed a linear relationship with alcohol. The odds ratios and 95% confidence intervals associated with abnormal values of the markers for the highest quintile of alcohol intake were 1.45 (1.06,1.97) for ApoB, 1.98 (1.40,2.80) for fasting glucose, and 1.74 (1.30,2.34) for body mass index. An inverse J-shaped relationship was assumed for ApoA1 and ApoB/ApoA1 ratio, whereas a U-shaped relationship was observed for serum triglycerides and mixed hyperlipidemia. Only the highest quintile of alcohol was associated with hypertension, although the test for linearity was also significant. No association was observed for Lp(a) or homocysteine. Associations were unmodified by further adjustment for carbohydrates, fiber, lipids, tobacco, or exercise. Conclusions: The aggregate of the disparate alcohol risk factor relationships suggests probable net benefit at 15 to 25 g of alcohol/day. [source] Effects of temperature and continuous and interrupted wetness on the infection of pear leaves by conidia of Venturia nashicolaPLANT PATHOLOGY, Issue 3 2005B.-H. Li Experiments were conducted to determine: (i) the effects of temperature and duration of continuous wet periods on the infection of pear seedlings by conidia of Venturia nashicola, the causal agent of pear scab; and (ii) the effects of the length and temperature of dry interrupting periods on the mortality of infecting conidia. Average number of scab lesions per leaf increased with increasing duration of wetness. Logistic models adequately described the change in the average number of scab lesions per leaf at 5, 10, 15, 20 and 25°C over the wetness duration. At 30°C, only a few lesions developed. Simple polynomial models satisfactorily described the relationship of the three logistic model parameters (maximum number of lesions, rate of appearance and the time to 50% of the maximum number of lesions) with temperature. The optimum temperature for infection was found to be approximately 20°C. The relationship between mortality and the length of a dry period interrupting an infection process can be satisfactorily described by an exponential model. The rate of mortality at 10, 16 and 22°C did not differ significantly, but was significantly less than that at 28°C. [source] Chronic disease risk in central New York dairy farmers: Results from a large health survey 1989,1999AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 1 2005Paul L. Jenkins PhD Abstract Background The agricultural workplace presents a variety of health and safety hazards; it is unknown whether farm work may be a risk factor for certain chronic diseases. Methods The health survey data from a large rural population in central New York were used from two studies (1989, 1999) to assess both 1999 prevalence and 10-year incidence of self-reported diabetes, heart disease, hypercholesterolemia, and hypertension among farm (predominantly dairy) and non-farm residents. The 1999 asthma prevalence was also assessed. Results Multiple logistic regression models for 1999 prevalence found statistically significant protective effects of farming for hypertension (OR,=,0.83, P,=,0.0105) and hypercholesterolemia (OR,=,0.853, P,=,0.0522). Non-significant results were seen for heart disease (OR,=,0.67, P,=,0.128) and diabetes (OR,=,0.856, P,=,0.1358). The model for 1999 asthma prevalence showed a significantly elevated risk for farming (OR,=,1.542, P,=,0.0004). Logistic models created for the 10-year incidence of hypertension, hypercholesterolemia, diabetes, and heart disease did not show a significant effect for farming. Conclusions The protective effect of farming observed for the 1999 prevalence of hypertension and hypercholesterolemia was not seen for the 10-year incidence of these diseases. Am. J. Ind. Med. 47:20,26, 2005. © 2004 Wiley-Liss, Inc. [source] Patch Occupancy and Potential Metapopulation Dynamics of Three Forest Mammals in Fragmented Afromontane Forest in South AfricaCONSERVATION BIOLOGY, Issue 4 2000Michael J. Lawes We recorded patch occupancy of blue duiker ( Philantomba monticola), tree hyrax ( Dendrohyrax arboreus), and samango monkey (Cercopithecus mitis labiatus) in 199 forest patches. Their rarity is ascribed to the fragmentation and destruction of their forest habitat. Incidence functions, derived from presence and absence data, were formulated as generalized linear models, and environmental effects were included in the fitted logistic models. The small and mostly solitary hyrax and duiker persisted in smaller patches than the large and social monkey. Although this result follows expectations based on relative home-range sizes of each species, the incidence probability of the samango monkey was invariant with increasing isolation, whereas a gradual decrease with increasing isolation was observed for the hyrax and duiker. Group dynamics may inhibit dispersal and increase the isolation effect in social species such as samango monkeys. A mainland-island metapopulation model adequately describes patterns of patch occupancy by the hyrax and duiker, but the monkeys' poor dispersal ability and obvious area-dependent extirpation suggest that they exist in transient, nonequilibrium (declining) metapopulations. Through identification of large forest patches for careful protection and management, the survival of all three species,especially the monkey,could be prolonged. Because no functional metapopulation may exist for the monkey, however, this is an emergency measure. For the duiker and hyrax, larger patches should form part of a network of smaller and closer patches in a natural matrix. Resumen: Investigamos la persistencia de tres mamíferos forestales raros de tamaño mediano (2,9 kg) en los bosques fragmentados de cinturón de niebla Podocarpus en la región central de la provincia KwaZulu-Natal, Sudáfrica. Registramos la ocupación del duiker azul ( Philantomba monticola), el hyrax arborícola ( Dendrohyrax arboreus) y el mono samango (Cercopithecus mitis labiatus) en 199 parches forestales. Su rareza se atribuye a la fragmentación y destrucción de su hábitat forestal. Las funciones de incidencia, derivadas de datos de presencia y ausencia, fueron formuladas como modelos lineales generalizados, y los efectos ambientales fueron incluidos en los modelos logísticos ajustados. Los pequeños y mayormente solitarios hyrax y duiker persistieron en parches más pequeños que los monos, que son más grandes y más sociables. A pesar de que este resultado obedece a expectativas basadas en tamaños de rango de hogar relativos de cada especie, la probabilidad de incidencia del mono samango no cambió con un incremento en el aislamiento, mientras que una disminución gradual al crecer el aislamiento se observó en hyrax y duiker. Las dinámicas de grupos podrían inhibir la dispersión e incrementar el efecto de aislamiento en especies sociables como lo es el mono samango. Un modelo de metapoblación continente-isla describe adecuadamente los patrones de la ocupación de parches por hyrax y duiker; sin embargo, la pobre capacidad de dispersión de los monos y la obvia extirpación área-dependente sugiere que estos existen en metapoblaciones transitorias, desequilibradas (en disminución). Mediante la identificación de parches forestales grandes para la protección y manejo cuidadosos, la supervivencia de las tres especies ( pero especialmente la de los monos) podría ser prolongada. Sin embargo, debido a que no existen metapoblaciones funcionales de monos, esta es una medida de emergencia. Para el duiker y el hyrax, los parches grandes deberán formar parte de una red de parches más pequeños y más cercanos en una matriz natural. [source] Does the economy affect teenage substance use?HEALTH ECONOMICS, Issue 1 2007Article first published online: 7 SEP 200, Jeremy Arkes Abstract This research examines how teenage drug and alcohol use responds to changes in the economy. In contrast to the recent literature confirming pro-cyclical alcohol use among adults, this research offers strong evidence that a weaker economy leads to greater teenage marijuana and hard-drug use and some evidence that a weaker economy also leads to higher teenage alcohol use. The findings are based on logistic models with state and year fixed effects, using teenagers from the NLSY-1997. The evidence also indicates that teenagers are more likely to sell drugs in weaker economies. This suggests one mechanism for counter-cyclical drug use , that access to illicit drugs is easier when the economy is weaker. These results also suggest that the strengthening economy in the 1990s mitigated what would otherwise have been much larger increases in teenage drug use. Copyright © 2006 John Wiley & Sons, Ltd. [source] The Effects of Geography and Spatial Behavior on Health Care Utilization among the Residents of a Rural RegionHEALTH SERVICES RESEARCH, Issue 1 2005Thomas A. Arcury Objective. This analysis determines the importance of geography and spatial behavior as predisposing and enabling factors in rural health care utilization, controlling for demographic, social, cultural, and health status factors. Data Sources. A survey of 1,059 adults in 12 rural Appalachian North Carolina counties. Study Design. This cross-sectional study used a three-stage sampling design stratified by county and ethnicity. Preliminary analysis of health services utilization compared weighted proportions of number of health care visits in the previous 12 months for regular check-up care, chronic care, and acute care across geographic, sociodemographic, cultural, and health variables. Multivariable logistic models identified independent correlates of health services utilization. Data Collection Methods. Respondents answered standard survey questions. They located places in which they engaged health related and normal day-to-day activities; these data were entered into a geographic information system for analysis. Principal Findings. Several geographic and spatial behavior factors, including having a driver's license, use of provided rides, and distance for regular care, were significantly related to health care utilization for regular check-up and chronic care in the bivariate analysis. In the multivariate model, having a driver's license and distance for regular care remained significant, as did several predisposing (age, gender, ethnicity), enabling (household income), and need (physical and mental health measures, number of conditions). Geographic measures, as predisposing and enabling factors, were related to regular check-up and chronic care, but not to acute care visits. Conclusions. These results show the importance of geographic and spatial behavior factors in rural health care utilization. They also indicate continuing inequity in rural health care utilization that must be addressed in public policy. [source] Accessibility of Addiction Treatment: Results from a National Survey of Outpatient Substance Abuse Treatment OrganizationsHEALTH SERVICES RESEARCH, Issue 3 2003Peter D. Friedmann Objectives This study examined organization-level characteristics associated with the accessibility of outpatient addiction treatment. Methods Program directors and clinical supervisors from a nationally representative panel of outpatient substance abuse treatment units in the United States were surveyed in 1990, 1995, and 2000. Accessibility was measured from clinical supervisors' reports of whether the treatment organization provided "treatment on demand" (an average wait time of 48 hours or less for treatment entry), and of whether the program turned away any patients. Results In multivariable logistic models, provision of "treatment on demand" increased two-fold from 1990 to 2000 (OR, 1.95; 95 percent CI, 1.5 to 2.6), while reports of turning patients away decreased nonsignificantly. Private for-profit units were twice as likely to provide "treatment on demand" (OR, 2.2; 95 percent CI, 1.3 to 3.6), but seven times more likely to turn patients away (OR, 7.4; 95 percent CI, 3.2 to 17.5) than public programs. Conversely, units that served more indigent populations were less likely to provide "treatment on demand" or to turn patients away. Methadone maintenance programs were also less likely to offer "treatment on demand" (OR, .65; 95 percent CI, .42 to .99), but more likely to turn patients away (OR, 2.4; 95 percent CI, 1.4 to 4.3). Conclusions Although the provision of timely addiction treatment appears to have increased throughout the 1990s, accessibility problems persist in programs that care for indigent patients and in methadone maintenance programs. [source] Analysis of serious non-AIDS events among HIV-infected adults at Latin American sitesHIV MEDICINE, Issue 9 2010WH Belloso Objective Acquired immune deficiency appears to be associated with serious non-AIDS (SNA)-defining conditions such as cardiovascular disease, liver and renal insufficiency and non-AIDS-related malignancies. We analysed the incidence of, and factors associated with, several SNA events in the LATINA retrospective cohort. Materials and methods Cases of SNA events were recorded among cohort patients. Three controls were selected for each case from cohort members at risk. Conditional logistic models were fitted to estimate the effect of traditional risk factors as well as HIV-associated factors on non-AIDS-defining conditions. Results Among 6007 patients in follow-up, 130 had an SNA event (0.86 events/100 person-years of follow-up) and were defined as cases (40 with cardiovascular events, 54 with serious liver failure, 35 with non-AIDS-defining malignancies and two with renal insufficiency). Risk factors such as diabetes, hepatitis B and C virus coinfections and alcohol abuse showed an association with events, as expected. The last recorded CD4 T-cell count prior to index date (P=0.0056, with an average difference of more than 100 cells/,L) and area under the CD4 cell curve in the year previous to index date (P=0.0081) were significantly lower in cases than in controls. CD4 cell count at index date was significantly associated with the outcome after adjusting for risk factors. Conclusions The incidence and type of SNA events found in this Latin American cohort are similar to those reported in other regions. We found a significant association between immune deficiency and the risk of SNA events, even in patients under antiretroviral treatment. [source] Predicting direction shifts on Canadian,US exchange rates with artificial neural networksINTELLIGENT SYSTEMS IN ACCOUNTING, FINANCE & MANAGEMENT, Issue 2 2001Jefferson T. Davis The paper presents a variety of neural network models applied to Canadian,US exchange rate data. Networks such as backpropagation, modular, radial basis functions, linear vector quantization, fuzzy ARTMAP, and genetic reinforcement learning are examined. The purpose is to compare the performance of these networks for predicting direction (sign change) shifts in daily returns. For this classification problem, the neural nets proved superior to the naïve model, and most of the neural nets were slightly superior to the logistic model. Using multiple previous days' returns as inputs to train and test the backpropagation and logistic models resulted in no increased classification accuracy. The models were not able to detect a systematic affect of previous days' returns up to fifteen days prior to the prediction day that would increase model performance. Copyright © 2001 John Wiley & Sons, Ltd. [source] Hospice Usage by Minorities in the Last Year of Life: Results from the National Mortality Followback SurveyJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 7 2003K. Allen Greiner MD OBJECTIVES: To examine racial/ethnic variations in rates of hospice use in a national cohort and to identify individual characteristics associated with hospice use. DESIGN: Secondary analysis of the 1993 National Mortality Followback Survey (NMFS), a nationally obtained sample using death certificates and interviews with relatives (proxy respondents) to provide mortality, social, and economic data and information about healthcare utilization in the last year of life for 23,000 deceased individuals. SETTING: Hospice care. PARTICIPANTS: Individuals aged 15 and older who died in 1993. Subjects were included in this analysis if they died of nontraumatic causes (N = 11,291). MEASUREMENTS: Hospice use was dichotomized by proxy responses indicating use or nonuse of home or inpatient hospice services. The percentage of individuals using hospice services in the last year of life was calculated. RESULTS: Unadjusted bivariate results found that African Americans were less likely to use hospice than whites (odds ratio (OR) = 0.59; P < .001) and that those without a living will (LW) (OR = 0.23; P < .001) and without a cancer diagnosis (OR = 0.28; P < .001) were less likely to use hospice. The negative relationship between African Americans and hospice use was unaffected when controlled for sex, education, marital status, existence of a LW, income, and access to health care. Logistic models revealed that presence of a LW diminished the negative relationship between African Americans and hospice use, but the latter remained significant (OR = 0.83; P = .033). A subanalysis of subjects aged 55 and older showed a significant interaction between access to care and race/ethnicity with respect to hospice use (P = .044). Inclusion of income in this multivariable logistic model attenuated the relationship between African-American race/ethnicity and hospice use (OR = 0.77), and the difference between whites and African Americans became only marginally statistically significant (P = .060). CONCLUSION: In the 1993 NMFS, hospice use was negatively associated with African-American race/ethnicity independent of income and access to healthcare. The relationship is not independent of age, insurance type, or history of stroke. For subjects aged 55 and older, access to healthcare may be an important confounder of the negative relationship between African-American race/ethnicity and hospice use. Consistent with previous studies, this analysis found that African Americans were less likely to use LWs than whites. The reduced importance of African-American race/ethnicity on hospice use with the inclusion of presence of a LW in logistic models suggests that similar cultural processes may shape differences between African Americans and whites in advance care planning and hospice use. [source] Individual response of growing pigs to lysine intakeJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 5 2009J. Heger Summary Nitrogen (N) balance experiment was carried out to study the individual and group response of growing pigs to lysine (Lys) intake. A series of 15 purified diets limiting in Lys were fed sequentially to nine pigs (initial body weight, 39 kg) during a 15-day experiment. Lysine concentration ranged from 50% to 140% of its assumed requirement. N retention in individual pigs was related to Lys intake using linear-plateau (LP) and quadratic-plateau (QP) models. No difference in the closeness of fit between the models was found (p = 0.72). There were significant differences between the slopes of individual regression lines in the LP model (p = 0.018) and between the individual plateau values in both models (p < 0.0001). The breakpoint values in the QP model were greater than those of the LP model (p = 0.027), while the plateau values estimated by both models were similar (p = 0.32). In the LP model, no relationship was found between the slopes and plateau values (p = 0.67, r = 0.17) or between the slopes and breakpoint values (p = 0.55, r = ,0.23), thus suggesting that pigs with higher protein deposition rate do not utilize lysine more efficiently. However, there was a close positive correlation between breakpoint and plateau values (p = 0.0005, r = 0.92). Based on LP and QP models, the mean daily requirement of Lys for a 47-kg gilt was estimated to be 20.8 and 24.2 g (0.79 and 0.92 g/MJ metabolizable energy), respectively, with coefficients of variation of approximately 10%. Marginal efficiency of Lys utilization derived from the LP model was 0.67 and was dependent on the range of input data selected. Lysine disappearance was a curvilinear function of Lys intake, indicating that Lys catabolism is not directly related to Lys intake. The closeness of fit of exponential, saturation kinetics or four-parameter logistic models applied to data set of all pigs was similar to that of LP or QP models. [source] Individual response of growing pigs to sulphur amino acid intakeJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 1 2008J. Heger Summary Two N balance experiments were conducted to study the individual response of growing pigs to limiting amino acid (AA) intake. Series of fifteen diets with increasing concentration of sulphur amino acids (SAA, Expt 1) or methionine in the presence of excess cystine (Expt 2) were fed sequentially to nine pigs during a 15-day experimental period. The concentration of the AA under test ranged from 50% to 140% of the requirement while other essential AA were given in a 25% excess relative to the limiting AA. N retention was related to the limiting AA intake using rectilinear and curvilinear models. In Expt 1, the quadratic-plateau model fitted the individual data significantly better (p = 0.01) than the linear-plateau model. No difference was found between the two models in Expt. 2, presumably due to the sparing effect of excess cystine on methionine utilization. Exponential, saturation kinetics or four-parameter logistic models fitted to data for all pigs showed that their goodness of fit was similar to those of quadratic-plateau or linear-plateau models. Significant differences (p < 0.05) were found between individual plateau values for N retention within each experiment while the slopes of the regression lines did not significantly differ either in Expt 1 (p = 0.07) or Expt 2 (p = 0.45). There was a positive correlation between the slope and plateau values of the linear-plateau model in Expt 1 (r = 0.74, p = 0.02) but no significant correlation was found in Expt 2 (r = ,0.48, p = 0.13). Marginal efficiencies of SAA and methionine utilization derived from the linear-plateau model were 0.43 and 0.65 respectively. Based on linear-plateau and quadratic-plateau models, daily requirements of SAA and methionine for a 50 kg pig were estimated to be 13.0 and 5.9 g and 14.3 and 6.1 g respectively. [source] Predicting time-specific changes in demographic processes using remote-sensing dataJOURNAL OF APPLIED ECOLOGY, Issue 2 2006HENRIK B. RASMUSSEN Summary 1Models of wildlife population dynamics are crucial for sustainable utilization and management strategies. Fluctuating ecological conditions are often key factors influencing both carrying capacity, mortality and reproductive rates in ungulates. To be reliable, demographic models should preferably rely on easily obtainable variables that are directly linked to the ecological processes regulating a population. 2We compared the explanatory power of rainfall, a commonly used proxy for variability in ecological conditions, with normalized differential vegetation index (NDVI), a remote-sensing index value that is a more direct measure of vegetation productivity, to predict time-specific conception rates of an elephant population in northern Kenya. Season-specific conception rates were correlated with both quality measures. However, generalized linear logistic models compared using Akaike's information criteria showed that a model based on the NDVI measure outperformed models based on rainfall measures. 3A predictive model based on coarse demographic data and the maximum seasonal NDVI value was able to trace the large variation in observed season-specific conception rates (Range 0,0·4), with a low median deviation from observed values of 0·07. 4By combining the model of season-specific conception rates with the average seasonal distribution of conception dates, the monthly number of conceptions (range 0,22) could be predicted within ±3 with 80% confidence. 5Synthesis and applications. The strong predictive power of the normalized differential vegetation index on time-specific variation in a demographic variable is likely to be generally applicable to resource-limited ungulate species occurring in ecologically variable ecosystems, and could potentially be a powerful factor in demographic population modelling. [source] Density dependence and population dynamics of black rhinos (Diceros bicornis michaeli) in Kenya's rhino sanctuariesAFRICAN JOURNAL OF ECOLOGY, Issue 3 2010Benson Okita-Ouma Abstract Density-dependent feedback mechanisms provide insights into the population dynamics and interactions of large herbivores with their ecosystem. Sex ratio also has particularly important implications for growth rates of many large mammal populations through its influence on reproductive potential. Therefore, the interrelationships between density-dependent factors, comprising density, sex ratio and underlying growth rates (r) were examined for the Eastern black rhino (Diceros bicornis michaeli) living in three rhino sanctuaries in Kenya using four population models. The exponential and logistic models gave similar results and the former were accepted because they better portrayed the actual situation on the ground. Sex ratios in all sanctuary populations were positively correlated with r but interpreted with realization of other factors also affecting r. We caution that the results of population models should be interpreted alongside ground-truthed observations. We recommend that future translocation strategies should take into account sex and age structures of the donor population, while future studies of density dependence should take into account both biotic and abiotic factors. Résumé Des mécanismes de feedback de densité-dépendance chez les grands herbivores donnent un aperçu de la dynamique des populations et de l'interaction avec l'écosystème. Les sex-ratios ont aussi d'importantes implications pour la dynamique des populations de nombreux grands mammifères, spécialement par leur influence sur le potentiel reproducteur. On a étudié ces relations croisées entre les facteurs densité-dépendants du rhino noir de l'Est Diceros bicornis michaeli, le sex-ratio et le taux de croissance (r) sous-jacent dans trois sanctuaires de rhinos du Kenya en utilisant quatre modèles de population. Les modèles exponentiel et logistique donnaient des résultats similaires, les résultats du premier étant acceptés parce qu'ils représentaient la situation actuelle sur le terrain. Les sex-ratios de toutes les populations étaient positivement liés àr mais interprétés en réalisant que d'autres facteurs affectent aussi r. Nous attirons l'attention sur le fait que les résultats de la modélisation des populations doivent être interprétés tout en les confirmant par des observations sur le terrain; nous recommandons des stratégies de translocations qui prélèvent des individus dans les diverses structures de sexe et d'âge de la population d'origine; et nous suggérons que de futures études de densité-dépendance tiennent compte de facteurs biotiques et abiotiques. [source] Lifestyle risk factors for intrahepatic stone: Findings from a case,control study in an endemic area, TaiwanJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 7pt1 2008Masato Momiyama Abstract Background and Aim:, To examine associations between lifestyle risk factors and intrahepatic stone (IHS), we conducted a case,control study in Taiwan, which has the highest incidence of IHS in the world. Methods:, Study subjects were 151 patients newly diagnosed with IHS at Chang Gung Memorial Hospital between January 1999 and December 2001. Two control subjects per case were selected randomly from patients who underwent minor surgery at the same hospital and from family members or neighbors of the hospital staff. Controls were matched to each case by age and gender. Information on lifestyle factors was collected using a self-administered questionnaire. Strength of associations was assessed using odds ratios derived from conditional logistic models. Results:, Female patients were significantly shorter than female controls. Compared to subjects with two or fewer children, odds ratios for those with six or more children were 20.4 in men (95% confidence interval, 1.89,221) and 2.82 (0.97,8.22) in women. Increasing level of education lowered the risk of intrahepatic stone (trend P = 0.004 for men and < 0.0001 for women). Women who had consumed ground-surface water for a long period had a somewhat increased risk (trend P = 0.05). Conclusion:, Lower socioeconomic status and poor hygiene may be involved in the development of intrahepatic stones. [source] Sampling bias and logistic modelsJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES B (STATISTICAL METHODOLOGY), Issue 4 2008Peter McCullagh Summary., In a regression model, the joint distribution for each finite sample of units is determined by a function px(y) depending only on the list of covariate values x=(x(u1),,,x(un)) on the sampled units. No random sampling of units is involved. In biological work, random sampling is frequently unavoidable, in which case the joint distribution p(y,x) depends on the sampling scheme. Regression models can be used for the study of dependence provided that the conditional distribution p(y|x) for random samples agrees with px(y) as determined by the regression model for a fixed sample having a non-random configuration x. The paper develops a model that avoids the concept of a fixed population of units, thereby forcing the sampling plan to be incorporated into the sampling distribution. For a quota sample having a predetermined covariate configuration x, the sampling distribution agrees with the standard logistic regression model with correlated components. For most natural sampling plans such as sequential or simple random sampling, the conditional distribution p(y|x) is not the same as the regression distribution unless px(y) has independent components. In this sense, most natural sampling schemes involving binary random-effects models are biased. The implications of this formulation for subject-specific and population-averaged procedures are explored. [source] Maximum likelihood estimation of bivariate logistic models for incomplete responses with indicators of ignorable and non-ignorable missingnessJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES C (APPLIED STATISTICS), Issue 3 2002Nicholas J. Horton Summary. Missing observations are a common problem that complicate the analysis of clustered data. In the Connecticut child surveys of childhood psychopathology, it was possible to identify reasons why outcomes were not observed. Of note, some of these causes of missingness may be assumed to be ignorable, whereas others may be non-ignorable. We consider logistic regression models for incomplete bivariate binary outcomes and propose mixture models that permit estimation assuming that there are two distinct types of missingness mechanisms: one that is ignorable; the other non-ignorable. A feature of the mixture modelling approach is that additional analyses to assess the sensitivity to assumptions about the missingness are relatively straightforward to incorporate. The methods were developed for analysing data from the Connecticut child surveys, where there are missing informant reports of child psychopathology and different reasons for missingness can be distinguished. [source] A model of non-isothermal degradation of nutrients, pigments and enzymesJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2004Maria G Corradini Abstract Published isothermal degradation curves for chlorophyll A and thiamine in the range 100,150 °C and the inactivation curves of polyphenol oxidase (PPO) in the range 50,80 °C could be described by the model C(t)/C0 = exp[,b(T)tn] where C(t) and C0 are the momentary and initial concentrations, respectively, b(T) a temperature dependent ,rate parameter' and n, a constant. This suggested that the temporal degradation/inactivation events of all three had a Weibull distribution with a practically constant shape factor. The temperature dependence of the ,rate parameter' could be described by the log logistic model, b(T) = loge[1 + exp[k(T , Tc)], where Tc is a marker of the temperature level where the degradation/inactivation occurs at a significant rate and k the steepness of the b(T) increase once this temperature range has been exceeded. These two models were combined to produce a non-isothermal degradation/inactivation model, similar to one recently developed for microbial inactivation. It is based on the assumption that the local slope of the non-isothermal decay curve, ie the momentary decay rate, is the slope of the isothermal curve at the momentary temperature at a time that corresponds to the momentary concentration of the still intact or active molecules. This model, in the form of a differential equation, was solved numerically to produce degradation/inactivation curves under temperature profiles that included heating and cooling and oscillating temperatures. Such simulations can be used to assess the impact of planned commercial heat processes on the stability of compounds of nutritional and quality concerns and the efficacy of methods to inactivate enzymes. Simulated decay curves on which a random noise was superimposed were used to demonstrate that the degradation/inactivation parameters, k and Tc, can be calculated directly from non-isothermal decay curves, provided that the validity of the Weibullian and log logistic models and the constancy of the shape factor n could be assumed. Copyright © 2004 Society of Chemical Industry [source] Bronchopulmonary dysplasia and brain white matter damage in the preterm infant: a complex relationshipPAEDIATRIC & PERINATAL EPIDEMIOLOGY, Issue 6 2009Luigi Gagliardi Summary We analysed the relationship between bronchopulmonary dysplasia (BPD) and brain white matter damage (WMD) in very preterm infants, adjusting for common risk factors and confounders. We studied a cohort of infants <32 weeks gestational age (GA) and <1500 g, admitted to 12 hospitals in Northern Italy in 1999,2002. The association between BPD and WMD was estimated by generalised estimating equations and conditional logistic models, adjusting for centre, GA, propensity score for prolonged ventilation and other potential confounders. Directed acyclic graphs (DAG) were used to depict the underlying causal structure and guide analysis. Of the 1209 infants reaching 36 weeks, 192 (15.8%) developed BPD (supplemental oxygen at 36 weeks) and 88 (7.3%) ultrasound-defined WMD (cystic periventricular leukomalacia). In crude analysis, BPD was a strong risk factor for WMD [odds ratio (OR) = 5.9]. With successive adjustments, the OR progressively decreased to 3.88 when adjusting for GA, to 2.72 adding perinatal risk factors, and further down to 2.16 [95% confidence interval 1.1, 3.9] when ventilation was also adjusted for. Postnatal factors did not change the OR. Significant risk factors for WMD, in addition to BPD, were a low GA, a lower Apgar score, a higher illness severity score, ventilation and early-onset sepsis, while antenatal steroids, being small for GA, and surfactant were associated with a reduced risk. In conclusion, our data suggest that BPD is associated with an increased risk of WMD; most of the effect is due to shared risk factors and causal pathways. DAGs helped clarify the complex confounding of this scenario. [source] Obesity and the prevalence of allergic diseases in schoolchildrenPEDIATRIC ALLERGY AND IMMUNOLOGY, Issue 6 2008Takashi Kusunoki Although the association between obesity and bronchial asthma (BA) has been gaining more attention, few studies have been conducted concerning the relationship between obesity and other allergic diseases. The objective of this study was to determine whether and how childhood obesity is associated with allergic diseases other than BA, such as atopic dermatitis (AD), allergic rhinitis (AR), allergic conjunctivitis (AC), and either AR or AC (AR/AC). A questionnaire was administered to the parents of 50,086 Japanese schoolchildren. Associations between childhood obesity and the various allergic diseases were evaluated by univariate and multivariate logistic models. Significant associations were found between higher body mass index (BMI) and AD (p = 0.03), and lower BMI and AC (p < 0.0001), and AR/AC (p < 0.0001). There was a significantly higher prevalence of BA in girls with obesity (p = 0.009) than in those without obesity. Significantly lower prevalence of AC (p = 0.01) and AR/AC (p = 0.002) among children with obesity, and AR (p = 0.04) and AR/AC (p = 0.0004) among boys with obesity were observed than those without obesity. Those who were obese and had AD were significantly more likely to have severe symptoms (p = 0.01). Overall, childhood obesity has positive associations with BA prevalence and AD severity, whereas it has negative associations with AR and AC prevalence, especially among boys. Changes in the immunologic balance accompanied by obesity might have different effects on each type of allergic disease. Exploring the mechanisms by which childhood obesity affects allergic status should lead to new management options for childhood allergy. [source] Disability and employment among U.S. working-age immigrantsAMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 4 2010Huiyun Xiang MD Abstract Background There is little research which examines disability status and the employment decisions of the US immigrant working-age population. Methods The 2007 American Community Survey data were analyzed to compare disabilities and employment characteristics between immigrant and US-born adults 18,64 years of age. Separate logistic regression models of employment were constructed among persons with disabilities and among persons without disabilities. Each multivariate model included nativity/citizenship, sex, race/ethnicity, age, and education. Results In 2007, 40.8% (95% CI: 39.9,41.7) of immigrants with disabilities were employed, while only 34.9% (95% CI: 34.6,35.2) of US-born persons with disabilities were employed. For each type of disability, including difficulty working, immigrants with disabilities were more likely than their US-born counterparts to be employed. The median wage/salary incomes for persons with disabilities, foreign-born and US-born, respectively, were $20,000 and $22,000. In contrast, the median wage/salary incomes of foreign-born persons with mental impairments, self-care limitations, or participation restrictions exceeded those of US-born persons with these same disabilities. Nativity and citizenship had different effects in separate logistic models of employment for persons with disabilities and persons without disabilities. Among persons with disabilities, foreign-born citizens were more likely to be employed than the US-born, OR,=,1.40 (95% CI: 1.33,1.48), and non-citizens were also more likely to be employed, OR,=,1.74 (95% CI: 1.62,1.87), than US-born persons. Among persons without disabilities, foreign-born non-citizens were less likely to be employed than the US-born, OR,=,0.82 (95% CI: 0.82,0.85). Conclusion Immigrants with disabilities were more frequently employed than US-born persons with disabilities for all types of disabilities. Am. J. Ind. Med. 53:425,434, 2010. © 2010 Wiley-Liss, Inc. [source] The Success of Continued Steroid Avoidance After Kidney Transplantation in the USAMERICAN JOURNAL OF TRANSPLANTATION, Issue 12 2009J. D. Schold There has been a significant increase in the use of steroid avoidance regimens as initial treatment for kidney transplant recipients. Early results of the effectiveness of this strategy has been mixed with certain prospective trials indicating increased acute rejection but population-based studies indicating similar or better graft survival as compared to steroid maintenance. We conducted a retrospective study of national registry data to evaluate risk factors for discontinuation of steroid avoidance protocols based on patient characteristics and concomitant immunosuppression. We evaluated 84 647 solitary kidney transplant recipients in the US with at least 6 months graft survival including 24 218 initially discharged without maintenance steroids. We utilized logistic models to assess risk factors for new initiation of steroids after initial steroid-avoidance and survival models to describe graft survival for patients after return to steroids. The most prominent risk factors for new initiation of steroids after deceased donor kidney transplantation included African-American race (AOR = 1.32, p < 0.01), retransplants (AOR = 1.81, p < 0.01), highly sensitized recipients (AOR = 1.29, p < 0.01), recipients with Medicaid (AOR = 1.85, p < 0.01), elevated HLA-MM (AOR = 1.26, p < 0.01) and older donor age (AOR = 1.19, p < 0.01). Concomitant medications were also significantly associated with the propensity to newly initiate steroids. Cumulatively the study suggests that both patient characteristics and concomitant medications are strongly associated with the success of steroid avoidance immunosuppressive regimens. [source] Dry season habitat use by critically endangered white-shouldered ibis in northern CambodiaANIMAL CONSERVATION, Issue 1 2010H. L. Wright Abstract We present the first scientific study of white-shouldered ibis Pseudibis davisoni habitat preferences in dry dipterocarp forest. Foraging sites included seasonal pools, forest understorey grasslands and fallow rice fields, with terrestrial sites used more following rainfall. Habitat and anthropogenic effects in logistic models of foraging site selection were examined by multimodel inference and model averaging. White-shouldered ibis preferred pools with greater cover of short vegetation (<25 cm) and less of the boundary enclosed, and forest sites with greater cover of bare substrate and lower people encounter rate. At forest sites, livestock density was positively related to bare substrate extent and thus may improve suitability for foraging ibis. At pools, livestock removed tall vegetation between the early and late dry season indicating their importance in opening up foraging habitats after wet season growth. However, by the late dry season, pools with greater livestock density had less short vegetation, the habitat favoured by ibis. Conservation strategies for white-shouldered ibis must consider a range of habitats, not just seasonal wetlands, and should incorporate extensive grazing and associated burning practises of local communities. Further understanding of the effects of these practices on vegetation, prey abundance and prey availability are therefore needed for effective conservation of this species. This will also develop our understanding of potentially beneficial anthropogenic influences in tropical environments. [source] Microvascular lesions in the brain and retina: The age, gene/environment susceptibility,Reykjavik study,ANNALS OF NEUROLOGY, Issue 5 2009Chengxuan Qiu MD Objective To investigate whether the severity and location of cerebral white matter hyperintensities (WMHs) and brain infarcts are correlated with the signs of retinal microvascular abnormalities in the elderly. Methods The study included 4,176 men and women (mean age, 76 years) who participated in the Age, Gene/Environment Susceptibility (AGES),Reykjavik Study. Digital retinal images of both dilated eyes were taken and evaluated for the presence of retinal focal arteriolar signs (focal arteriolar narrowing and arteriovenous nicking) and retinopathy lesions (retinal blot hemorrhages and microaneurysms). Brain magnetic resonance imaging scans were acquired and evaluated for the presence and distribution of cerebral infarcts and WMHs. Logistic and multinomial logistic models were constructed to estimate the association of retinal microvascular signs to brain lesions. Results Controlling for demographic and major cardiovascular risk factors, we found that retinal focal arteriolar signs, but not retinopathy lesions, were significantly associated with an increasing load of subcortical and periventricular WMHs. The strongest association was found between retinal arteriolar signs and a heavier WMH load, specifically in the subcortical frontal lobe, and periventricular frontal and parietal caps. There was a tendency toward bilateral retinal focal arteriolar narrowing being more strongly associated with the heavier load of subcortical WMHs. Arteriovenous nicking was significantly associated with subcortical infarcts. Interpretation In older adults, retinal focal arteriolar signs, but not retinopathy lesions, are correlated with the load of diffuse WMHs, particularly those located in the subcortical frontal lobe, and the periventricular frontal and parietal caps of the brain. Ann Neurol 2009;65:569,576 [source] Logistic Equations Effectively Model Mammalian Cell Batch and Fed-Batch Kinetics by Logically Constraining the FitBIOTECHNOLOGY PROGRESS, Issue 4 2005Chetan T. Goudar A four-parameter logistic equation was used to fit batch and fed-batch time profiles of viable cell density in order to estimate net growth rates from the inoculation through the cell death phase. Reduced three-parameter forms were used for nutrient uptake and metabolite/product formation rate calculations. These logistic equations constrained the fits to expected general concentration trends, either increasing followed by decreasing (four-parameter) or monotonic (three-parameter). The applicability of this approach was first verified for Chinese hamster ovary (CHO) cells cultivated in 15-L batch bioreactors. Cell density, metabolite, and nutrient concentrations were monitored over time and used to estimate the logistic parameters by nonlinear least squares. The logistic models fit the experimental data well, supporting the validity of this approach. Further evidence to this effect was obtained by applying the technique to three previously published batch studies for baby hamster kidney (BHK) and hybridoma cells in bioreactors ranging from 100 mL to 300 L. In 27 of the 30 batch data sets examined, the logistic models provided a statistically superior description of the experimental data than polynomial fitting. Two fed-batch experiments with hybridoma and CHO cells in benchtop bioreactors were also examined, and the logistic fits provided good representations of the experimental data in all 25 data sets. From a computational standpoint, this approach was simpler than classical approaches involving Monod-type kinetics. Since the logistic equations were analytically differentiable, specific rates could be readily estimated. Overall, the advantages of the logistic modeling approach should make it an attractive option for effectively estimating specific rates from batch and fed-batch cultures. [source] | |||||||||||||||||||