title: A comparative review of methods for comparing means using partially paired data.
abstract: In medical experiments with the objective of testing the equality of two means, data are often partially paired by design or because of missing data. The partially paired data represent a combination of paired and unpaired observations. In this article, we review and compare nine methods for analyzing partially paired data, including the two-sample t-test, paired t-test, corrected z-test, weighted t-test, pooled t-test, optimal pooled t-test, multiple imputation method, mixed model approach, and the test based on a modified maximum likelihood estimate. We compare the performance of these methods through extensive simulation studies that cover a wide range of scenarios with different effect sizes, sample sizes, and correlations between the paired variables, as well as true underlying distributions. The simulation results suggest that when the sample size is moderate, the test based on the modified maximum likelihood estimator is generally superior to the other approaches when the data is normally distributed and the optimal pooled t-test performs the best when the data is not normally distributed, with well-controlled type I error rates and high statistical power; when the sample size is small, the optimal pooled t-test is to be recommended when both variables have missing data and the paired t-test is to be recommended when only one variable has missing data.
authors.affiliation: 1 Department of Experimental Statistics, Louisiana State University, Baton Rouge, LA, USA.
authors.forename: Beibei
authors.initials: B
authors.lastname: Guo
authors.affiliation: 2 Department of Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.|3 School of Statistics, Xi'an University of Finance and Economics, Xi'an, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Yuan
mesh_terms: D003627:Data Interpretation, Statistical; D017051:Hospice Care; D006801:Humans; D017567:Karnofsky Performance Status; D016013:Likelihood Functions; D012107:Research Design; D018401:Sample Size
keywords: Partially paired; maximum likelihood; missing data; optimal weight; paired t-test; pre-post comparison