SUGGESTED ANSWER TO QUESTION 2A-2

In looking for extraneous variables, you need to think of ways, other than educational level, in which the various groups of people may differ. Here are three possibilities (you may have thought of others).

It seems likely that people who spend more time in school would score higher on IQ tests, on average, than people who spend less time in school. Thus, intelligence would be one important extraneous variable. It seems probable that more intelligent people would tend to receive higher annual earnings than less intelligent people.

It also seems likely that people who spend more time in school are more motivated to be successful, on average, than people who spend less time in school. Thus, motivation would be another important extraneous variable. It seems probable that more motivated people would tend to receive higher annual earnings than less motivated people.

Finally, it seems likely that people who spend more years in school will generally have parents in the higher socioeconomic levels of society. Such parents should be more able, on average, to help their children both financially and socially (that is, they will have more influential contacts), which should increase the chances that their children will be able to obtain jobs that pay more money.

Thus, there are factors other than the amount of education received that could explain why people with more years of schooling make more money, on average, than people with fewer years of schooling. It is possible that the amount of schooling has little to do with average annual earnings. Of course, this analysis doesn't mean that schooling is irrelevant to how much money one makes. It simply means that there are extraneous variables that would need to be controlled if one wanted to make the argument that more schooling causes people to make more money.