BACKGROUND:The range of demographic, behavioral and health characteristics of cohort subjects recruited via the Internet is not yet well established.
OBJECTIVES:To examine the distributions of characteristics of a cohort recruited via the Internet and compare to a probabilitybased national sample.
METHODS: Prospective Obesity Cohort of Economic Evaluation Determinants (PROCEED) is an ongoing multinational observational cohort of normal weight (body mass index [BMI] 20- 24 kg/m2), overweight (BMI 25-29.9 kg/m2) and obese subjects (BMI ≥30 kg/m2). Recruited through an existing Internet panel, subjects had to be 35-75 years of age; not pregnant; if overweight or obese, willing to lose weight in next 12 months; and weigh <180 kg. Recruitment was stratified to balance gender within overweight and obese categories. Respondents with BMI ≥25 kg/m2 were pooled and regrouped by abdominal obesity status (AO), defined as waist circumference (WC) greater than 102cm for men and 88cm for women. We compared demographics and selected health and behavior characteristics from the PROCEED US cohort with estimates from a subset of the US National Health and Nutrition Examination Survey (NHANES) 2001-2002 who were in the same age, BMI and WC ranges and not pregnant. For the PROCEED sample, we calculated unadjusted sample means and percentages, but for NHANES we calculated weighted means and percentages taking into account the survey design.
RESULTS: In all 3 subgroups (100 normal weight subjects, 293 without AO, and 674 subjects with AO) the PROCEED cohort was similar to the NHANES population in terms of mean age, marital status, behavior (alcohol consumption, smoking status and physical activity) and prevalence of self-reported conditions such as high cholesterol and diabetes. All 3 subgroups were proportionally more white in PROCEED. Mixed results were seen for education, income, and hypertension (e.g., the proportion of PROCEED subjects reporting income >75,000 USD was lower for normal weight, higher for subjects without AO and similar for subjects with AO versus NHANES).
CONCLUSIONS: A diverse cohort with broad similarities to a national sample can be recruited via the Internet; stratified sampling of minorities may be desired in some studies.
