12.23 The effects of two stimulant drugs. An experimenter was interested in investigating the effects of two stimulant drugs (labeled A and B). She divided 25 rats equally into five groups (placebo, Drug A low, Drug A high, Drug B low, and Drug B high) and, 20 minutes after injection of the drug, recorded each rat’s activity level (higher score is more active). The following table summarizes the results:
| Treatment | s2 | |
|---|---|---|
| Placebo | 11.80 | 17.20 |
| Low A | 15.25 | 13.10 |
| High A | 18.55 | 10.25 |
| Low B | 16.15 | 7.75 |
| High B | 17.10 | 12.50 |
(a) Plot the means versus the type of treatment. Does there appear to be a difference in the activity level? Explain.
(b) Is it reasonable to assume that the variances are equal? Explain your answer, and if reasonable, compute sp.
(c) Give the degrees of freedom for the F statistic.
(d) The F statistic is 2.64. Find the associated P-value and state your conclusions.