title: Characteristics of physical measurement consent in a population-based survey of older adults.
abstract: BACKGROUND
  Collecting physical measurements in population-based health surveys has increased in recent years, yet little is known about the characteristics of those who consent to these measurements.
  
  
  OBJECTIVE
  To examine the characteristics of persons who consent to physical measurements across several domains, including one's demographic background, health status, resistance behavior toward the survey interview, and interviewer characteristics.
  
  
  METHODS
  We conducted a secondary data analysis of the 2006 Health and Retirement Study, a nationally-representative panel survey of older adults aged 51 and older. We performed multilevel logistic regressions on a sample of 7457 respondents who were eligible for physical measurements. The primary outcome measure was consent to all physical measurements.
  
  
  RESULTS
  Seventy-nine percent (unweighted) of eligible respondents consented to all physical measurements. In weighted multilevel logistic regressions controlling for respondent demographics, current health status, survey resistance indicators, and interviewer characteristics, the propensity to consent was significantly greater among Hispanic respondents matched with bilingual Hispanic interviewers, patients with diabetes, and those who visited a doctor in the past 2 years. The propensity to consent was significantly lower among younger respondents, those who have several Nagi functional limitations and infrequently participate in "mildly vigorous" activities, and those interviewed by black interviewers. Survey resistance indicators, such as number of contact attempts and interviewer observations of resistant behavior in prior wave iterations of the Health and Retirement Study were also negatively associated with physical measurement consent. The propensity to consent was unrelated to prior medical diagnoses, including high blood pressure, cancer (excluding skin), lung disease, heart abnormalities, stroke, and arthritis, and matching of interviewer and respondent on race and gender.
  
  
  CONCLUSIONS
  Physical measurement consent is not strongly associated with one's health status, though the findings are somewhat mixed. We recommend that physical measurement results be adjusted for characteristics associated with the likelihood of consent, particularly functional limitations, to reduce potential bias. Otherwise, health researchers should exercise caution when generalizing physical measurement results to the population at large, including persons with functional limitations that may affect their participation.
authors.affiliation: Institute for Social Research, University of Michigan, Ann Arbor, MI 48104-1248, USA. joesaks@umich.edu
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Sakshaug
authors.forename: Mick P
authors.initials: MP
authors.lastname: Couper
authors.forename: Mary Beth
authors.initials: MB
authors.lastname: Ofstedal
mesh_terms: D000367:Age Factors; D000368:Aged; D005260:Female; D006304:Health Status; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D010808:Physical Examination / Q000379:methods* / Q000706:statistics & numerical data*; D012959:Socioeconomic Factors