A physiologist has conducted an experiment to examine the effects of a newly discovered hormone (called hormone X) on aggression. Ten rats were injected with hormone X, and 10 other rats received a placebo injection (the control group). The number of aggressive behaviors was counted for each rat in the study.

The following results were obtained:

• Hormone X Group: Mean aggressive behaviors = 8.4, s = 1, n = 10
• Control (placebo) Group: Mean aggressive behaviors = 5.6, s = 1.2, n = 10
• We will use = .05, two-tailed test

What type of t- test should be used?

Group of answer choices

Repeated measures (i.e., paired samples)t-test

Independent samplest-test

Z test

correlation