Bioindicators in the MIDUS national study: protocol, measures, sample, and comparative context.

Objectives: Midlife in the United States (MIDUS) is a national study of health and aging among individuals aged 25 to 74 at baseline (1995-1996). Longitudinal survey assessments (2004-2005), were followed by biological assessments on a subsample (aged 35-85).To facilitate public use, we describe the protocol, measures, and sample.

Method: Respondents traveled to clinics for a 2-day data-collection protocol that included fasting blood specimens, 12-hr urine specimen, medical history, physical exam, bone densitometry, and a laboratory challenge (heart rate variability, blood pressure, respiration, salivary cortisol).

Results: Response rates for the biological protocol (N = 1,255) were 39.3% or 43.1% (adjusting for those who could not be located or contacted). Reasons for nonparticipation were travel, family obligations, and being too busy. Respondents were comparable to the recruitment pool on most demographic characteristics and health assessments.

Discussion: Strengths of the protocol vis-à-vis similar studies include opportunities to link biological factors with diverse content from other MIDUS projects.