Quynh Nguyen

We describe bias resulting from individualized treatment selection, which occurs when treatment has heterogeneous effects and individuals selectively choose treatments of greatest benefit to themselves. This pernicious bias may confound estimates from observational studies and lead to important misinterpretation of intent-to-treat analyses of randomized trials. Despite the potentially serious threat to inferences, individualized treatment selection has rarely been formally described or assessed. The Moving to Opportunity (MTO) trial randomly assigned subsidized rental vouchers to low-income families in high-poverty public housing. We assessed the Kessler-6 psychological distress and Behavior Problems Index outcomes for 2,829 adolescents 4-7 years after randomization. Among families randomly assigned to receive vouchers, we estimated probability of moving (treatment), predicted by pre-randomization characteristics (c-statistic=0.63). We categorized families into tertiles of this esti...

In the United States, where coronary heart disease (CHD) is the leading cause of mortality, CHD risk assessment is a priority and accurate blood pressure (BP) measurement is essential. Hypertension estimates in the National Longitudinal Study of Adolescent Health (Add Health), Wave IV (2008)-a nationally representative field study of 15,701 participants aged 24-32-was referenced against NHANES (2007-2008) participants of the same age. We examined discordances in hypertension, and estimated the accuracy and reliability of blood pressure in the Add Health study. Hypertension rates (BP: ≥ 140/90 mm Hg) were higher in Add Health compared with NHANES (19% vs. 4%), but self-reported history was similar (11% vs. 9%) among adults aged 24-32. Survey weights and adjustments for differences in participant characteristics, examination time, use of antihypertensive medications, and consumption of food/caffeine/cigarettes before blood pressure measurement had little effect on between-study differences in hypertension estimates. Among Add Health participants interviewed and examined twice (full and abbreviated interviews), blood pressure was similar, as was blood pressure at the in-home and in-clinic examinations conducted by NHANES III (1988-1994). In Add Health, there was minimal digit preference in blood pressure measurements; mean bias never exceeded 2 mm Hg; and reliability (estimated as intraclass correlation coefficients) was 0.81 and 0.68 for systolic and diastolic BPs, respectively. The proportion of young adults in NHANES reporting a history of hypertension was twice that with measured hypertension, whereas the reverse was found in Add Health. Between-survey differences were not explained by digit preference, low validity, or reliability of Add Health blood pressure data, or by salient differences in participant selection, measurement context, or interview content. The prevalence of hypertension among Add Health Wave IV participants suggests an unexpectedly high risk of cardiovascular disease among US young adults and warrants further scrutiny.