Question 5. Bisphenol-A (BPA) is a chemical that is present in many diverse products, including canned food and reusable water bottles. Because animal experiments suggest that BPA may be an endocrine disruptor, a group of pediatricians decided to conduct a case-control study on BPA exposure and precocious (early) puberty in girls. 150 cases with precocious puberty and 150 controls were identified and enrolled from among patients at a children’s clinic. 60 cases and 20 controls had high urinary BPA levels; the remainder had normal urinary BPA levels. a. Set up the 2×2 table using these data. (2 points)
The correct answer is the 2×2 table below.
| Urinary BPA level | Cases (precocious puberty) | Controls | Total |
|—|—:|—:|—:|
| High BPA | 60 | 20 | 80 |
| Normal BPA | 90 | 130 | 220 |
| Total | 150 | 150 | 300 |
Explanation: 150 cases total with 60 high and 90 normal; 150 controls with 20 high and 130 normal; row and column totals shown.