Statistical review of 95 studies employing repeated-measures analysis of variance published in the Korean Journal of Anesthesiology.

tinues to be used widely for the analysis of repeated-measures data in anesthetic research. RMANOVA, like other parametric statistical tests, specifies several assumptions and requires specific description in publications. A recent article in the Korean Journal of Anesthesiology (KJA) provided valid information on RMANOVA [1]. We reviewed 493 studies published in KJA between January 2010 and December 2014. A total of 95 studies (19.3%) employed RMANOVA to analyze repeated-measures data. We reviewed these studies and summarized the following: type of variables, statistical assumptions (normally distributed population, homogeneity of variances, and sphericity assumption), interaction between two factors in the results, sample size calculation, post-hoc testing, and type of statistical package used. In addition to a dependent variable (e.g. blood pressure), all the studies (n = 95) contained one within-subject factor (e.g. different measurement sites, such as left and right arm, or a time series post-treatment, such as 0, 10, and 20 minutes in the same participant) as an independent variable. Some of these studies (n = 35) also contained one between-subject factor (e.g. different drugs or dosages administered to randomly assigned participants) as an additional independent variable. When a study involves one within-subject factor only, one-way RMANOVA is required, while “two-way RMANOVA” should be used for those that contain one within-subject factor and one between-subject factor. However, there is some confusion regarding the exact definition of “two-way RMANOVA,” although it is the most frequently used term in most KJA publications. A “true” twoway RMANOVA (or two-way ANOVA with repeated-measures in two factors) compares mean differences between data sets, split into “two within-subject factors.” Each data set is collected at one measurement point (one within-subject factor) under one treatment condition (another within-subject factor). For example, if every participant has their blood pressure measured three times (“the first within-subject factor”; for example, just before injection, just after injection, and 1 minute after injection) under propofol, thiopental sodium, and ketamine induction (“the second within-subject factor”), 2 weeks apart, nine data sets will be collected from a single group of participants. However, in anesthetic research, the participants are frequently randomized into two or more separate treatment conditions (e.g. each participant receives propofol, thiopental sodium, or ketamine induction [“between-subject factor”] and their blood pressure is measured three times [“within-subject factor”]); therefore, nine data sets will be collected from three groups of participants. Consequently, researchers should consider the differences between the “two-way RMANOVA” and the “two-way ANOVA with repeated-measures in one factor (also called mixed-model Letter to the Editor