Exposure data were collected cross-sectionally at one point in time, yet exposures are subject to temporal variation. This issue becomes particularly important when examining health effects of non-persistent short-lived environmental pollutants, such as BPA and phthalates. A recent study of urinary BPA and type-2 diabetes using three NHANES cycles found a significant association which was confirmed in one cycle (2003–2004) but not in the other two cycles. This finding indicates possible exposure misclassification due to a single urine sample [70]. Reliable exposure biomarker data assessed based on repeatedly collected samples is warranted to reduce exposure misclassification.
