An article in the current issue of the American Journal of Epidemiology is about participants in a large health survey. It compares people who turned in the questionnaire via the Web with those who answered via mail.
Over 50% of 77,047 participants chose to enroll in the study via the Web . . . The authors compared the demographic and health characteristics of Web responders with those of paper responders. Web responders were slightly more likely to be male, to be younger, to have a high school diploma or college degree, and to work in information technology or another technical occupation. Web responders were more likely to be obese and to smoke more cigarettes and were less likely to be problem alcohol drinkers and to report occupational exposures.
The study began in 2001.