Exercise 10: Income, Religiosity, and the Presidential Vote
Another example of the joint influence of two independent variables involves the impact of two different social or demographic characteristics on the vote — income and religiosity. To examine the effects of these variables on the presidential vote, generate two basic two-variable tables — one for the relationship between income (R05) and the presidential vote (Table 10A), and one for the relationship between church attendance (R09) and the presidential vote (Table 10B). For the reasons suggested in Exercise 1, you should use the recoded version of A02 that you created for that exercise, so that you examine only the major-party vote (i.e., only the Obama and Romney voters).
These tables show that both income and church attendance are related to the vote. Republicans do better among both those with higher incomes and those who are more religious. Does this mean that Republicans will do extremely well among those who have a high income level and a high level of church attendance? Do both of these variables equally affect the vote, or is one a more important influence? To examine these questions, generate a table that uses both income and church attendance as independent variables and presidential vote as the dependent variable. To simplify the table, recode R05 and R09 so that they are categorized into high, medium, and low. In this case, it does not matter whether the recoded version of R05 is treated as the independent variable and the recoded version of R09 is the control variable or the reverse, as we are considering both to be independent variables that jointly affect the vote.