40 rats were given divided randomly into four groups and assigned to one of four treatments: placebo, drug A, drug B, or both drug A and drug B. Response is a standard measure of physiological arousal.
A data frame with 40 observations, 10 in each of 4 columns the corresponding to placebo, drug A, drug B and both drug A and drug B; no NAs.
Rats receiving a placebo treatment.
Rats receiving only drug A.
Rats receiving only drug B.
Rats receiving both drug A and drug B.