Are children with higher exposure to pesticides more likely to develop ADHD (attention-deficit/hyperactivity disorder)? In a recent study, authors measured levels of urinary dialkyl phosphate (DAP, a common pesticide) concentrations and ascertained ADHD diagnostic status (Yes/No) for 1139 children who were representative of the general US population. The subjects were divided into two groups based on high or low pesticide concentrations, and we compare the proportion with ADHD in each group.
(a) Define the relevant parameter(s) and state the null and alternative hypotheses.
(b) In the sample, children with high pesticide levels were more likely to be diagnosed with ADHD. Can we necessarily conclude that, in the population, children with high pesticide levels are more likely to be diagnosed with ADHD? (Whether or not we can make this generalization is, in fact, the statistical question of interest.)
(c) To assess statistical significance, we assume the null hypothesis is true. What does that mean in this case? State your answer in terms of pesticides and ADHD.
(d) The study found the results to be statistically significant. Which of the hypotheses, H₀ or H_a, is no longer a very plausible possibility?
(e) What do the statistically significant results imply about pesticide exposure and ADHD?