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Estimation Equations (estimation + equation)
Kinds of Estimation Equations Selected AbstractsWeight Change and Lower Body Disability in Older Mexican AmericansJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 10 2005Soham Al Snih MD Objectives: To examine the association between 2-year weight change and onset of lower body disability over time in older Mexican Americans. Design: Data were from the Hispanic Established Population for the Epidemiological Study of the Elderly (1993,2001). Weight change was examined by comparing baseline weight to weight at 2-year follow-up. Incidence of lower body disability was studied from the end of this period through an additional 5 years. Setting: Five southwestern states: Texas, New Mexico, Colorado, Arizona, and California. Participants: One thousand seven hundred thirty-seven noninstitutionalized Mexican-American men and women aged 65 and older who reported no limitation in activities of daily living (ADLs) and were able to perform the walk test at 2-year follow-up. Measurements: In-home interviews assessed sociodemographic factors, self-reported physician diagnoses of medical conditions (arthritis, diabetes mellitus, heart attack, stroke, hip fracture, and cancer), self-reported ADLs, depressive symptoms, and number of hospitalizations. Cognitive function, handgrip muscle strength, and body mass index (BMI) were obtained. The outcomes were any limitation of lower body ADL (walking across a small room, bathing, transferring from a bed to a chair, and using the toilet) and limitation on the walk test over subsequent 5-year follow-up period. General Estimation Equation (GEE) was used to estimate lower body disability over time. Results: Weight change of 5% or more occurred in 42.3% of the participants; 21.7% lost weight, 20.6% gained weight, and 57.7% had stable weight. Using GEE analysis, with stable weight as the reference, weight loss of 5% or more was associated with greater risk of any lower body ADL limitation (odds ratio (OR)=1.43, 95% confidence interval (CI)=1.06,1.95) and walking limitation (OR=1.35, 95% CI=1.03,1.76) after controlling for sociodemographic variables and BMI at baseline. Weight gain of 5% or more was associated with greater risk of any lower body ADL limitation (OR=1.39, 95% CI=1.02,1.89), after controlling for sociodemographic variables and BMI at baseline. When medical conditions, handgrip muscle strength, high depressive symptomatology, cognitive function, and hospitalization were added to the equation, the relationship between 2-year weight change (>5% loss or >5% gain) and lower body disability decreased. Conclusion: Health conditions and muscle strength partially mediate the association between weight loss or gain and future loss of ability to walk and independently perform ADLs. [source] Prognostic Factors for the Surgery for Mesial Temporal Lobe Epilepsy: Longitudinal AnalysisEPILEPSIA, Issue 8 2005Sang-Wuk Jeong Summary:,Purpose: Determining long-term prognostic factors of surgery for mesial temporal lobe epilepsy (MTLE) is important for identifying ideal candidates and predicting the prognosis for individual patients. We tried to identify the prognostic factors of anterior temporal lobectomy (ATL) for MTLE with longitudinal multivariate analysis. Methods: Two hundred twenty-seven patients with MTLE were included in this study. The primary outcome variable was patient status 1,5 years after surgery: seizure free, or not. Clinical characteristics and recent diagnostic modalities were considered as prognostic factors. Univariate and standard multiple logistic-regression analysis for outcome at 1 and 5 years after surgery and the generalized estimation equation (GEE) model for longitudinal multiple logistic regression of the 5-year follow-up period were used. Results: The seizure-free rate at 1 year was 81.1% and decreased to 75.2% at 5 years after surgery. By the univariate or standard multiple logistic-regression analysis, age at surgery or hippocampal sclerosis on magnetic resonance imaging (MRI) ipsilateral to surgery was significant for the postsurgical outcome. However, the longitudinal analysis by the GEE model revealed that younger age at surgery [odds ratio (OR), 0.59; 95% confidence interval (CI), 0.43,0.81], absence of secondarily generalized tonic,clonic seizure (2°GTCS; OR, 0.45; 95% CI, 0.26,0.79), and hippocampal sclerosis on MRI (OR, 2.44; 95% CI, 1.11,5.26) were significant predictors of a good surgical outcome. Conclusions: Age at surgery, presence of 2°GTCS, and hippocampal sclerosis on MRI are independent prognostic factors for ATL in MTLE. These findings suggest that MTLE is a progressive disorder, and surgical outcome is better when early ATL is performed. [source] Low-Dose Topiramate Versus Lamotrigine in Migraine Prophylaxis (The Lotolamp Study)HEADACHE, Issue 3 2007Praveen Gupta MD Objective.,To assess the efficacy and safety of topiramate and lamotrigine for prophylaxis in patients with frequent migraine as compared to each other and to placebo. Methods.,Sixty patients with frequent migraine (more than 4 attacks per month) from the headache clinic at a tertiary referral centre in India were randomized to receive 50 mg topiramate/lamotrigine or matching placebo for 1 month each in 2 divided doses in 4 phases in a crossover manner with a washout period of 7 days in between. Primary efficacy measure was responder rate (50% decrease in mean migraine frequency/intensity). Secondary efficacy measures included reduction in mean monthly frequency, intensity, duration, rescue medication use, migraine associated symptoms, and adverse events. Statistical analysis.,Analysis was on intention to treat basis. Data were analyzed as correlated data. Generalized estimation equation was used to compute overall mean standard deviation and 95% confidence intervals for each of the outcome variables. Bonferroni's correction done for multiple comparisons. P value of <.017 was taken as significant. Results.,Fifty-seven patients comprised the intent-to-treat population. Four patients withdrew from the study at various phases, none because of the side effects. Responder rate for frequency was significantly higher for topiramate versus placebo (63% vs 30%, P < .001), and versus lamotrigine (63% vs 46 %, P= .02). For intensity of headache also a responder rate of topiramate versus placebo (50% vs 10%, P < .001), and versus lamotrigine (50% vs 41%, P= .01) was observed. Topiramate showed statistically significant benefits (P < .017) in most of the secondary efficacy measures while lamotrigine was beneficial for reduction in headache frequency, and migraine associated symptoms. Adverse events were similar. Conclusion.,Low-dose topiramate is efficacious in migraine prophylaxis as compared to both placebo and lamotrigine. Lamotrigine in low doses might be beneficial for headache frequency; however, longer trials are required to establish its efficacy on the intensity and frequency of migraine. [source] Variable Selection for Semiparametric Mixed Models in Longitudinal StudiesBIOMETRICS, Issue 1 2010Xiao Ni Summary We propose a double-penalized likelihood approach for simultaneous model selection and estimation in semiparametric mixed models for longitudinal data. Two types of penalties are jointly imposed on the ordinary log-likelihood: the roughness penalty on the nonparametric baseline function and a nonconcave shrinkage penalty on linear coefficients to achieve model sparsity. Compared to existing estimation equation based approaches, our procedure provides valid inference for data with missing at random, and will be more efficient if the specified model is correct. Another advantage of the new procedure is its easy computation for both regression components and variance parameters. We show that the double-penalized problem can be conveniently reformulated into a linear mixed model framework, so that existing software can be directly used to implement our method. For the purpose of model inference, we derive both frequentist and Bayesian variance estimation for estimated parametric and nonparametric components. Simulation is used to evaluate and compare the performance of our method to the existing ones. We then apply the new method to a real data set from a lactation study. [source] Two Typical Examples of Scaling Ionic Partition Scheme for Estimating Correlation Energy of A2 Type MoleculesCHINESE JOURNAL OF CHEMISTRY, Issue 4 2004Shu-Ping Zhuo Abstract Based on the calculation results of pair correlation energy contributions of the various electron pairs in Naz and H2NNH2 systems and the application of the scaling ionic partition scheme for symmetrical A2 type systems, the total correlation energies of Na2 and H2NNH2 have been reproduced by using this simple scheme. The two results show that the absolute deviations are within an acceptable range of mr, however, in this way, more than 90% of computational work can be. saved. The most attractive result in present paper is that, in these two molecules the coefficients c1 and c2 in the estimation equation can be obtained by the proportion of correlation energy of A, to that of A+ singlet system. Therefore, it is believed that the proposed ionic partition scheme for symmetrical A2 molecules would be very useful to estimate the correlation energies of large symmetrical molecules. [source] The impact of changing nicotine replacement therapy licensing laws in the United Kingdom: findings from the International Tobacco Control Four Country SurveyADDICTION, Issue 8 2009Lion Shahab ABSTRACT Aim To evaluate the impact of a new licence for some nicotine replacement therapy products (NRT) for cutting down to stop (CDTS) on changes in the pattern of NRT use. Design Quasi-experimental design comparing changes in NRT use across two waves of a population-based, replenished-panel, telephone survey conducted before and after the introduction of new licensing laws in the United Kingdom with changes in NRT use in three comparison countries (Australia, Canada and United States) without a licensing change. Participants A total of 7386 and 7013 smokers and recent ex-smokers participating in the 2004 and/or 2006/7 survey. Measurements Data were collected on demographic and smoking characteristics as well as NRT use and access. In order to account for interdependence resulting from some participants being present in both waves, generalized estimation equations with an exchangeable correlation matrix were used to assess within-country changes and linear and logistic regressions to assess between-country differences in adjusted analyses. Findings NRT use was more prevalent in the United Kingdom and increased across waves in all countries but no wave × country interaction was observed. There was no evidence that the licensing change increased the prevalence of CDTS or the use of NRT (irrespective of how it was accessed) for CDTS in the United Kingdom relative to comparison countries. There was also no evidence for a change in concurrent smoking and NRT use among smokers not attempting to stop in the United Kingdom relative to comparison countries. Conclusion The addition of the CDTS licence for some NRT products in the United Kingdom appears to have had very limited, if any, impact on NRT use in the first year after the licence change. [source] Subject and informant characteristics influence the reliability and validity of family history information: an analysis based on the generalized estimating equations approachINTERNATIONAL JOURNAL OF METHODS IN PSYCHIATRIC RESEARCH, Issue 2 2000Reinhard Heun Abstract Family history information is a necessary surrogate for unavailable interview information in family studies. However, the reliability and validity of such information has rarely been assessed during the conduct of family studies. This paper presents a reanalysis of data on the reliability and validity of family history information for dementia and depression using the general estimation equations approach. All available relatives of patients and controls were interviewed and questioned about the psychiatric morbidity of other family members. Interinformant reliability of this family history information was evaluated as well as factors influencing this information. The validity of family history was investigated by comparing the informant derived diagnoses with interview-derived diagnoses. To account for possible lack of independence of family history provided by several family members on other family members, the generalized estimating equations (GEE) were used in statistical analysis. The interinformant reliability for depression (kappa = 0.13) was low. It was fair for dementia (kappa = 0.34). The informants more frequently agreed about the diagnosis of dementia when the subject was older. The sensitivity of family history was 35.2% for dementia and 31.8% for depression. The specificity of family history information was generally above 97%. The sensitivity of family history increased significantly with the severity of both disorders. The sensitivity of the family history for dementia was higher when the informant was a first-degree relative, when he was younger and when the index subject of the family suffered from dementia. The specificity of the family history was slightly reduced with higher age. The observed low sensitivity of family history information leads to underestimation of psychiatric disorders. The informants provide more useful information on more severe disorders. The sensitivity of family history was higher in families with an affected index subject than in control families, so familial aggregation of dementia might be overestimated in studies using the family history method. Copyright © 2000 Whurr Publishers Ltd. [source] Benzodiazepines and injury: a risk adjusted model,,PHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 1 2005Dustin D. French MA Abstract Background Benzodiazepines (BZD) are one class of medications that are generally acknowledged to be a risk factor for injuries. Objective Our objective was to link outpatient prescription data with clinical data in order to develop a risk adjusted binary model that associates BZD usage with the risk for a healthcare encounter for an injury. Methods In total, 3 years of outpatient BZD prescription data, totaling 133,872 outpatient BZD prescriptions for 13,745 patients for a VA medical center, were combined with data from inpatient and outpatient administrative databases. The model incorporated Elixhauser comorbidity measures with 1-year look back period, along with hospital discharges, marital status, age, mean arterial pressure and body mass index. The model also included the dose of the drug, converted to valium equivalents and its duration. The model was analyzed using generalized estimation equations (GEE). Results Dose, duration, discharges and various comorbidities were associated with an increased risk for injury, while being married reduced the risk. Increased body mass was associated with increased injury risk. Increased mean arterial pressure was associated with decreased risk. Conclusions These findings offer guidance on how specific combinations of risk factors and potential protective effects may impact accidental injury risk. Clinicians prescribing or adjusting BZDs can use these results to more accurately tailor medication regimens for a patient. Our findings suggest that clinicians should also consider the nature of the social support system available to the patient in assessing total injury risk. Copyright © 2004 John Wiley & Sons, Ltd. [source] Stature estimation formulae for indigenous North American populationsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2010Benjamin M. Auerbach Abstract Stature estimation methods for adult indigenous humans from the Americas have generally relied on a limited number of regression equations. The available equations, however, are not broadly applicable to the diversity of the populations that lived in the New World prior to European colonization. Furthermore, some equations that have been used were originally derived from inappropriate reference samples, such as the "Mongoloid" group measured by Trotter and Gleser (Am J Phys Anthropol 16 [1958] 79-123). This study develops new stature estimation equations for long bones of the lower limb from a geographically diverse sample of North American archaeological sites. Statures were reconstructed from 967 skeletons from 75 archaeological sites using the revised Fully anatomical technique (Raxter et al., Am J Phys Anthropol 130 [2006] 374-384). Archaeological samples were grouped according to general body proportions, using relative tibia and femur length to stature as guides. On the basis of differences in these proportions, three broad groupings were identified: a high latitude "arctic" group, a general "temperate" group, and a Great Plains group. Sex-specific ordinary least squares regression formulae were developed based on femoral and tibial lengths for each of these groups. Comparisons of the new stature estimation equations with previously available equations were conducted using several archaeological test samples. In most cases, the new stature estimation equations are more precise than those previously available, and we recommend their use throughout most of North America. The equations developed by Genovés for Mesoamerican and US Southwest samples are a useful alternative for these regions. Applicability of the new equations to South American samples awaits further testing. Am J Phys Anthropol, 2010. © 2009 Wiley-Liss, Inc. [source] Associations among adolescent risk behaviours and self-esteem in six domainsTHE JOURNAL OF CHILD PSYCHOLOGY AND PSYCHIATRY AND ALLIED DISCIPLINES, Issue 8 2004Lauren G. Wild Background:, This study investigated associations among adolescents' self-esteem in 6 domains (peers, school, family, sports/athletics, body image and global self-worth) and risk behaviours related to substance use, bullying, suicidality and sexuality. Method:, A multistage stratified sampling strategy was used to select a representative sample of 939 English-, Afrikaans- and Xhosa-speaking students in Grades 8 and 11 at public high schools in Cape Town, South Africa. Participants completed the multidimensional Self-Esteem Questionnaire (SEQ; DuBois, Felner, Brand, Phillips, & Lease, 1996) and a self-report questionnaire containing items about demographic characteristics and participation in a range of risk behaviours. It included questions about their use of tobacco, alcohol, cannabis, solvents and other substances, bullying, suicidal ideation and attempts, and risky sexual behaviour. Data was analysed using a series of logistic regression models, with the estimation of model parameters being done through generalised estimation equations. Results:, Scores on each self-esteem scale were significantly associated with at least one risk behaviour in male and female adolescents after controlling for the sampling strategy, grade and race. However, specific self-esteem domains were differentially related to particular risk behaviours. After taking the correlations between the self-esteem scales into account, low self-esteem in the family and school contexts and high self-esteem in the peer domain were significantly independently associated with multiple risk behaviours in adolescents of both sexes. Low body-image self-esteem and global self-worth were also uniquely associated with risk behaviours in girls, but not in boys. Conclusions:, Overall, the findings suggest that interventions that aim to protect adolescents from engaging in risk behaviours by increasing their self-esteem are likely to be most effective and cost-efficient if they are aimed at the family and school domains. [source] | ||||||||||