Comparison of two tests useful in situations where treatment is expected to increase variability relative to controls.
The type I error and power characteristics of the modified t test were compared with those of the generalized t test. Results suggested that, in contrast to the generalized t test, the modified t test can be seriously non-robust to departures from population normality, with such departures often producing anti-conservative results. Neither test held an absolute power advantage over the other when responses were from normal distributions, but the modified t test was generally more powerful for these conditions. In comparison with the pooled samples t test, both tests were usually much more efficient when treatment caused increases both in mean response and between-subject variance, and suffered only small disadvantages when between-subject variance was unchanged by treatment. Given these results and other considerations, recommendations for use of these recently devised tests are given.
Blair
R C
RC
Department of Community and Family Health, College of Public Health, University of South Florida.
Sawilowsky
S
S
D015982:Bias; D016009:Chi-Square Distribution; D015987:Effect Modifier, Epidemiologic; D016018:Least-Squares Analysis; D016015:Logistic Models; D015201:Meta-Analysis as Topic; D009010:Monte Carlo Method; D016011:Normal Distribution; D015203:Reproducibility of Results; D012494:Sampling Studies; D016896:Treatment Outcome