The joy of social science lies in the discovery of relationships between variables. Following the Wheel of Science allows us to think about how one variable may cause changes in another variable. Using theory to propose hypotheses lets us see if variables impact each other. Up to this point we’ve relied on looking at simple relationships that link an independent variable with a dependent variable. In thinking about how one variable causes changes to another variable, however, it is seldom the case that only one variable is involved.
Let’s go back to our earlier discussion regarding the relationship between education and income. Is it really that education, alone, causes changes to income? We noted previously that if we didn’t believe that education impacts income, we would not invest the time and money it takes to earn a college degree. Think again about the inconsistencies (the negative cases) within the relationship between education and income. Your professors with PhDs have the highest levels of formal education. Yet those earning the most money in our society tend to be celebrities and sports figures, many of whom do not even have college educations. If those who make the most money are not the most highly educated, why do we continue to place such an emphasis on getting more education, assuming it causes higher levels of income?
When we think about causes, we’re looking at variables that produce a change in another variable. Thus far we’ve focused on single independent ...