For his Statistics class experiment, researcher J. Gilbert decided to study how parents' income affects children's performance on standardized tests like the SAT. He proposed to collect information from a random sample of test takers and examine the relationship between parental income and SAT score.
a) Is this an experiment? If not, what kind of study is it?
b) If there is a relationship between parental income and SAT score, why can't we conclude that differences in score are caused by differences in parental income?