A sociologist conducts interviews with former protestors and activists in order to study the struggles of the civil rights movement. A political scientist reviews survey data on the political views of the student population on her campus in order to study the correlation between class (freshman, sophomore, junior, senior) and political affiliation. A pediatrician randomly assigns babies to two different groups, giving one group a new type of infant formula and the other group conventional formula, in order to study the effects of the new formula. The issue of confounding variables is more likely to be present in data sets than in data sets