For particular studies, subsamples are drawn at random from the panel. We do not use volunteers. People aren't dropped from the sample pool after each survey. Thus some respondents may be interviewed several times over the course of a year. That raises the possibility of panel effects, which are changes in attitudes or behavior that occur simply because an individual is participating in a panel study.
Rivers says past research into panel effects has been inconclusive.
But they monitor their panel members and constantly refresh the potential respondent poll so as to avoid respondent fatigue. So far, cooperation rates have been astonishing. Most people initially contacted agree to accept the equipment, and in two Post Internet surveys, the return rate has averaged about 80 percent. The overall cooperation rate which factors in those who initially refused to accept the equipment and join the panel-is comfortably over 50 percent, far better than on standard telephone surveys. If InterSurvey hammers its respondent base with repeated questionnaires, chances are good that both the quality of the interviews and the participation rate will fall.