Annals of biometrics & biostatistics最新文献

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A Bivariate Mixed Model Approach in Characterizing the Evolution of Longitudinal Body Mass Index and Quality of Life Processes in Adolescents with Severe Obesity Following Bariatric Surgery: A 5-year follow-up of the TeenLABS cohort. 双变量混合模型方法表征肥胖手术后严重肥胖青少年纵向体重指数和生活质量过程的演变:对TeenLABS队列的5年随访。

Annals of biometrics & biostatistics Pub Date : 2020-01-01 Epub Date: 2020-07-13

Jane Khoury, Todd M Jenkins, Shelley Ehrlich, Richard Boles, Marc P Michalsky, Thomas H Inge, Rhonda D Szczesniak

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引用次数: 0

Conservative Sample Size Determination for Repeated Measures Analysis of Covariance. 协方差重复测量分析中保守样本量的确定。

Annals of biometrics & biostatistics Pub Date : 2013-07-05

Timothy M Morgan, L Douglas Case

{"title":"Conservative Sample Size Determination for Repeated Measures Analysis of Covariance.","authors":"Timothy M Morgan, L Douglas Case","doi":"","DOIUrl":"","url":null,"abstract":"In the design of a randomized clinical trial with one pre and multiple post randomized assessments of the outcome variable, one needs to account for the repeated measures in determining the appropriate sample size. Unfortunately, one seldom has a good estimate of the variance of the outcome measure, let alone the correlations among the measurements over time. We show how sample sizes can be calculated by making conservative assumptions regarding the correlations for a variety of covariance structures. The most conservative choice for the correlation depends on the covariance structure and the number of repeated measures. In the absence of good estimates of the correlations, the sample size is often based on a two-sample t-test, making the 'ultra' conservative and unrealistic assumption that there are zero correlations between the baseline and follow-up measures while at the same time assuming there are perfect correlations between the follow-up measures. Compared to the case of taking a single measurement, substantial savings in sample size can be realized by accounting for the repeated measures, even with very conservative assumptions regarding the parameters of the assumed correlation matrix. Assuming compound symmetry, the sample size from the two-sample t-test calculation can be reduced at least 44%, 56%, and 61% for repeated measures analysis of covariance by taking 2, 3, and 4 follow-up measures, respectively. The results offer a rational basis for determining a fairly conservative, yet efficient, sample size for clinical trials with repeated measures and a baseline value.","PeriodicalId":90101,"journal":{"name":"Annals of biometrics & biostatistics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2013-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4100335/pdf/nihms-580617.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"32522068","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0