Understanding Experiments with Two Groups - Answer Key
Twenty Sets $1 =$

Essay

Understanding Experiments with Two Groups - Answer Key
Twenty sets of depressed twins are obtained for a study on the effects of a new antidepressant. In each twin set, one twin is assigned to receive the drug, and the other is designed to receive the placebo. Three months later, depression levels are measured on a scale from 1 (not at all depressed) to 7 (very depressed). The following data was obtained:
GROUP $1 =$ Received drug
GROUP $2 =$ Received placebo
Variable $=$ Depression level
$\begin{array} { l l l l } \text { GROUP } & N & \text { Mean } & S D \\ \text { GROUP 1 } & 10 & 3.21 & 1.035 \\ \text { GROUP 2 } & 10 & 5.77 & 1.772 \\ t = 5.785 & d f = 9 & p = 0.017 & \text { Cohen's } d = .88 \end{array}$
-Is the effect size small, medium, or large? How do you know?