In Exercise 4.16 on page 232, we describe an observational study investigating a possible relationship between exposure to organophosphate pesticides as measured in urinary metabolites (DAP) and diagnosis of ADHD (attention-deficit/hyperactivity disorder). In reporting the results of this study, the authors make the following statements:

• ‘‘The threshold for statistical significance was set at P < .05.”

• ‘‘The odds of meeting the . . . criteria for ADHD increased with the urinary concentrations of total DAP metabolites.”

• ‘‘The association was statistically significant.”

(a) What can we conclude about the p-value obtained in analyzing the data?

(b) Based on these statements, can we distinguish whether the evidence of association is very strong vs moderately strong? Why or why not?

(c) Can we conclude that exposure to pesticides is related to the likelihood of an ADHD diagnosis?

(d) Can we conclude that exposure to pesticides causes more cases of ADHD? Why or why not?  

Exercise 4.16

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.