- An overestimate of true folate intake among Mexican American women would have made effects appear weaker than they were
- The FFQ doesn’t distinguish postconception time from preconception time
- Many women adhere to a healthier diet during pregnancy
- These women may have selectively recalled healthy (folate-rich) foods consumed after the neural tube closed (~1 month postconception) rather than their more relevant preconception intake
- If case and control women misclassified their exposures to the same extent, estimated odds ratios would have been biased towards the null