Active Trader compared earnings on stock investments when companies made strong pre-earnings announcements versus cases where pre-earnings announcements were weak. Both sample sizes were 28.
The average performance for the strong preearnings announcement group was 0.19%, and the average performance for the weak pre-earnings group was 0.72%.
The standard deviations were 5.72% and 5.10%, respectively.5 Conduct a test for equality of means using α = 0.01 and construct a 99% confidence interval for difference in means.