StatisticsdrillEffect size: Cohen's d
A statistics problem from Statisticsdrill. Solve it with one answer box, with a fresh sample on every attempt and the worked steps and spreadsheet function in the answer, and it is checked the moment you submit.
The task
Two onboarding programs are compared on a skills test. Program A: n = 39, x̄ = 79.2, s = 9.1. Program B: n = 47, x̄ = 73.7, s = 7.3. What is Cohen's d for the difference (A minus B), using the pooled standard deviation? Round to 2 decimal places.
What this problem teaches
By the usual rule of thumb, 0.2 is a small effect, 0.5 medium and 0.8 large. Unlike a t statistic, d does not grow with the sample size.
A hint if you get stuck
d = (x̄1 - x̄2) / s_p, where s_p² = [(n1 - 1)s1² + (n2 - 1)s2²] / (n1 + n2 - 2). It is the difference measured in standard deviations.
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