Comparison of two tests useful in situations where treatment is expected to increase variability relative to controls

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Abstract
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.