A researcher conducts an experiment to examine how serotonin (a chemical involved in neural processes) is related to aggression. One sample of rats serves as a control group and receives a placebo that does not affect normal serotonin levels. A second sample of rats receives a drug that lowers brain levels of serotonin. Then the researcher tests the animals by recording the number of aggressive responses each of the rats displays. The data are as follows:

Control Low serotonin

n = 10 n = 15

M = 12 M = 19

SS = 200 SS = 352

What kind of hypothesis test is appropriate here: single-sample z-test; single-sample t-test; or independent-samples t-test? (answer with only one of these!)

What is the independent or quasi-independent variable?

What is the dependent variable (the construct; not how it's measured)?

How is the dependent variable measured?

For the two questions below, if you decide to write hypotheses in terms of parameters, use the word mu rather than trying to type a Greek letter, please.

Write the null hypothesis in words or parameters (your choice)?

Write the alternative hypothesis in words or parameters (your choice)

What is the critical value of the test statistic, assuming α = .05? Be sure that this is consistent with whether H1 is one- or two-tailed.

If you used df to find this value, please report it. If you did not need to use df to find this value, enter the number 0.