Infections Can Lower IQ A headline in June 2015 proclaims "Infections can lower IQ." The headline is based on a study in which scientists gave an IQ test to Danish men at age 19. They also analyzed the hospital records of the men and found that $35 %$ of them had been in a hospital with an infection such as an STI or a urinary tract infection. The average IQ score was lower for the men who had an infection than for the men who hadn't.

(a) What are the cases in this study?

(b) What is the explanatory variable? Is it categorical or quantitative?

(c) What is the response variable? Is it categorical or quantitative?

(d) Does the headline imply causation?

(e) Is the study an experiment or an observational study?

(f) Is it appropriate to conclude causation in this case?