A simple question for research studies to address is whether two variables tend to vary with each other such that higher frequencies of one variable are associated with either higher or lower frequencies of the other variable. Such associations might be interesting whether they apply to academic attributes (e.g., the association between reading comprehension and mathematics calculations), behavioral attributes (e.g., the association between prosocial behavior and juvenile delinquency), or physiological attributes (e.g., the association between weight and diabetes), as well as in other areas. Such questions do not address the reasoning for the associations. They often are a starting point for research in an area. Before using relatively costly methods such as randomized control trials (RCTs, described in Chapter 5) or single case designs (SCDs, described in Chapter 8) to test whether changes in an independent variable (IV) cause changes in a dependent variable (DV), it may first be desirable to use less costly correlational and causal comparative studies.