In 2000, a study was conducted on 4000 Swedish 15-year-old males. The boys were surveyed and asked, among other things, how often they consume fish each week. Three years later, these answers were linked to the boys’ scores as 18-year-olds on an intelligence test. The study found that boys who consume fish at least once a week scored higher on the intelligence test.
(a) Is this an experiment or an observational study? Explain.
(b) What are the explanatory and response variables?
(c) Give an example of a potential confounding factor.
(d) Does this study provide evidence that eating fish once a week improves cognitive ability?