Home About us Contact
|
Home About us Contact | ||
|
|
||
Composite Variable (composite + variable)
Selected AbstractsFlea species richness and parameters of host body, host geography and host ,milieu'JOURNAL OF ANIMAL ECOLOGY, Issue 6 2004BORIS R. KRASNOV Summary 1We have assessed how different host parameters affect species richness of flea assemblages using the independent contrasts method. Three groups of host parameters were examined. The first group included host body parameters (body size, basal and average daily metabolic rates), the second group included parameters of geographical range size and position of this range in relation to the equator (latitude) and the third group comprised parameters related to the number of sympatric closely related species. 2None of the host body parameters correlated with species richness of flea assemblages. 3Flea species richness increased with an increase in latitude of the geographical range centre of a host as well as with an increase in a composite variable that described the size of the geographical range. 4The number of sympatric closely related species both across the entire geographical range and locally was correlated positively with species richness of fleas. 5Our results show that species richness of ectoparasites is affected little by parameters of the host body and to a greater extent by parameters related to the host environment. [source] Addressing Three Common Issues in Research on Youth Activities: An Integrative Approach for Operationalizing and Analyzing InvolvementJOURNAL OF RESEARCH ON ADOLESCENCE, Issue 3 2010Michael A. Busseri Youth activity involvement has been operationalized and analyzed using a wide range of approaches. Researchers face the challenges of distinguishing between the effects of involvement versus noninvolvement and intensity of involvement in a particular activity, accounting simultaneously for cumulative effects of involvement, and addressing multiple unique effects of individual activities. In the present work, we review and illustrate the conceptual and empirical implications of these issues using data from a study of activity involvement and successful development in early adolescence (N=537; M age=11.56, 52% female). An integrative solution is introduced based on a latent composite variable (LCV) model (Bollen & Lennox, 1991), which can be used to address all three issues simultaneously. Using this approach, we show that of the aggregate indices examined, breadth of involvement was uniquely and positively associated with multiple indices of successful development. Of the individual activities, a dichotomous score and residual frequency rating for involvement in out-of-school clubs were both uniquely associated with less positive development indicators. We concluded that an LCV approach provides a novel method for addressing several fundamental operational and analytic issues facing researchers who investigate youth activity involvement as a context for positive development. [source] Dose selection and population pharmacokinetics of PEG-Intron in patients with chronic myelogenous leukaemiaBRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Issue 3 2007Samir Gupta Aims To assess the dose selection using population pharmacokinetics of Pegylated Intron-,2b (PEG-Intron) in patients with chronic myelogenous leukaemia (CML). Methods PEG-Intron 3,6 µg kg,1 was administered subcutaneously once a week and blood samples were collected up to 48 weeks of treatment. A total of 624 samples collected from 137 patients were included in the analysis. Nonlinear mixed-effects modelling was used to analyse the sparsely sampled concentration data from a clinical efficacy trial. Covariates in the analysis included weight, sex, age, race, serum creatinine and estimated creatinine clearance (CLcr). Results The apparent clearance of PEG-Intron decreased after repeated dosing. The clearance at treatment week 4 was 42.3 l day,1 (patients with CLcr 120 ml min,1) with interpatient variability 30%. At treatment week 48, the clearance value was reduced to 69% of its week 4 value. CLcr, a composite variable calculated from body weight, sex, age and serum creatinine, had a small but statistically significant influence on the clearance of PEG-Intron. The clearance of PEG-Intron in patients with CML was 40% higher than that of hepatitis C virus-infected patients. Conclusion The dose of PEG-Intron 6.0 µg kg,1 week,1 appeared appropriate in the treatment of patients with CML. [source] Plant species richness of nature reserves: the interplay of area, climate and habitat in a central European landscapeGLOBAL ECOLOGY, Issue 4 2002Petr Py Abstract Aim To detect regional patterns of plant species richness in temperate nature reserves and determine the unbiased effects of environmental variables by mutual correlation with operating factors. Location The Czech Republic. Methods Plant species richness in 302 nature reserves was studied by using 14 explanatory variables reflecting the reserve area, altitude, climate, habitat diversity and prevailing vegetation type. Backward elimination of explanatory variables was used to analyse the data, taking into account their interactive nature, until the model contained only significant terms. Results A minimal adequate model with reserve area, mean altitude, prevailing vegetation type and habitat diversity (expressed as the number of major habitat types in the reserve) accounted for 53.9% of the variance in species number. After removing the area effect, habitat diversity explained 15.6% of variance, while prevailing vegetation type explained 29.6%. After removing the effect of both area and vegetation type, the resulting model explained 10.3% of the variance, indicating that species richness further increased with habitat diversity, and most obviously towards warm districts. After removing the effects of area, habitat diversity and climatic district, the model still explained 9.4% of the variance, and showed that species richness (i) significantly decreased with increasing mean altitude and annual precipitation, and with decreasing January temperature in the region of the mountain flora, and (ii) increased with altitudinal range in regions of temperate and thermophilous flora. Main conclusions We described, in quantitative terms, the effects of the main factors that might be considered to be determining plant species richness in temperate nature reserves, and evaluated their relative importance. The direct habitat effect on species richness was roughly equal to the direct area effect, but the total direct and indirect effects of area slightly exceeded that of habitat. It was shown that the overall effect of composite variables such as altitude or climatic district can be separated into particular climatic variables, which influence the richness of flora in a context-specific manner. The statistical explanation of richness variation at the level of families yielded similar results to that for species, indicating that the system of nature conservation provides similar degrees of protection at different taxonomic levels. [source] Preparing a large data set for analysis: using the Minimum Data Set to study perineal dermatitisJOURNAL OF ADVANCED NURSING, Issue 4 2005Kay Savik MS Aim., The aim of this paper is to present a practical example of preparing a large set of Minimum Data Set records for analysis, operationalizing Minimum Data Set items that defined risk factors for perineal dermatitis, our outcome variable. Background., Research with nursing home elders remains a vital need as ,baby boomers' age. Conducting research in nursing homes is a daunting task. The Minimum Data Set is a standardized instrument used to assess many aspects of a nursing home resident's functional capability. United States Federal Regulations require a Minimum Data Set assessment of all nursing home residents. These large data would be a useful resource for research studies, but need to be extensively refined for use in most statistical analyses. Although fairly comprehensive, the Minimum Data Set does not provide direct measures of all clinical outcomes and variables of interest. Method., Perineal dermatitis is not directly measured in the Minimum Data Set. Additional information from prescribers' (physician and nurse) orders was used to identify cases of perineal dermatitis. The following steps were followed to produce Minimum Data Set records appropriate for analysis: (1) identification of a subset of Minimum Data Set records specific to the research, (2) identification of perineal dermatitis cases from the prescribers' orders, (3) merging of the perineal dermatitis cases with the Minimum Data Set data set, (4) identification of Minimum Data Set items used to operationalize the variables in our model of perineal dermatitis, (5) determination of the appropriate way to aggregate individual Minimum Data Set items into composite measures of the variables, (6) refinement of these composites using item analysis and (7) assessment of the distribution of the composite variables and need for transformations to use in statistical analysis. Results., Cases of perineal dermatitis were successfully identified and composites were created that operationalized a model of perineal dermatitis. Conclusion., Following these steps resulted in a data set where data analysis could be pursued with confidence. Incorporating other sources of data, such as prescribers' orders, extends the usefulness of the Minimum Data Set for research use. [source] Using the composite variables of reproductive morphology, histology and steroid hormones to determine age and size at sexual maturity for the thorny skate Amblyraja radiata in the western Gulf of MaineJOURNAL OF FISH BIOLOGY, Issue 5 2006J. A. Sulikowski Age at size was linked to sexual maturity in 77 male and 93 female thorny skates Amblyraja radiata from the western Gulf of Maine using three criteria: 1) gross reproductive morphology, 2) histology and 3) steroid hormone concentrations. Age-bias plots and the coefficient of variation from vertebral band counts suggested that the ageing method represented a non-biased and precise approach to the age assessment of A. radiata. Maturity ogives for males, based on data gathered for clasper length, circulating testosterone concentrations and proportion of mature spermatocysts within the testes, predicted that 50% maturity occurred at a total length (LT) of 865 mm and c. 10·90 years of age. For females, maturity ogives, based on data gathered for ovary mass, shell gland mass, follicle size and circulating oestradiol concentrations, predicted that 50% maturity occurred at 875 mm LT and c. 11·00 years of age. Collectively, the results suggest that analysis of several contemporaneous reproductive variables offers an accurate determination of sexual maturity in the thorny skate. [source] | |||||||||||||