Understanding Experiments with Two Groups
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 were obtained:
GROUP 1 = Received drug
GROUP 2 = Received placebo
Variable = Depression level
GROUP N Mean SD
GROUP 1 10 3.21 1.035
GROUP 2 10 5.77 1.772
t = 5.785 df = 9 p = 0.017 Cohen’s d = .88
- What is the independent variable?
The independent variable is new antidepressant.
- What is the dependent variable?
The dependent variable is depressed twins.
- What is the scale of measurement for the dependent variable?
The scale of measurement for the dependent variable is depression level.
- What kind of research design was used?
The research design that was used was an observational study.
- What kind of statistical analysis was used?
The statistical analysis that was used was the “Two sample t test with equal variances”.
- Is the effect size small, medium, or large? How do you know?
The effect size is large. It is large because it is very close to 1.
- Write an APA-format conclusion.
