1. Professor Wang wants to test the hypothesis that people's history of incarceration will have negative consequences for their self-regard. He administers a survey to a random sample of 609 Michigan residents who at some point had been registered with the Michigan Department of Corrections. (Over 1,000 people were asked to participate, but those who refused did not differ in characteristics from those who did participate.) Prof. Wang correlates respondents' length of time spent in a correctional facility with their scores on the Rosenberg Self-Esteem Scale. He finds a statistically significant, negative correlation between the two variables. He concludes that incarceration does indeed cause decreased self-esteem.

In a paragraph, comment on the internal validity of this design and conclusion. Is this a valid conclusion? Why or why not?