A pro-life group wanted to test the effectiveness of an antiabortion commercial. Two random samples, each of 250 respondents, were recruited in Atlanta. One group was shown the antiabortion commercial. Then, attitudes toward abortion were measured for respondents in both groups.

a) Identify the independent and dependent variables in this experiment.

b) What type of design was used?

c) What are the potential threats to internal and external validity in this experiment?

d) In the experiment just described, suppose the respondents had been selected by convenience rather than randomly. What

type of design would result?