Preliminary tests of equality of variances before comparing data are not recommended by statisticians. A study showed that using a two-stage procedure with a Levene test followed by a t test can lead to errors and worsen the situation. The Welch test is better than the t test when variances are unequal. Small sample sizes, slight differences in variances, and stricter significance levels can all impact error rates. Using a separate-variances test whenever sample sizes are unequal provides the best protection.