Results and effect of refusal recontact in a case-control study of ectopic pregnancy

In a population-based study of ectopic pregnancy, a card-back system of initial subject contact yielded a positive response from 85.1% of potential cases and 65.0% of potential controls. We subsequently recontacted by telephone potential controls who had declined to participate and offered them $10 compensation for participation. We recontacted 205 of the 330 control women who had refused to participate. Twenty-eight were found to be ineligible, and 75.7% of the remaining 177 agreed to participate on recontact. The additional 125 women were not recontacted, 9 because of firm initial refusals and 116 because the study ended before contact could be sought or made. Controls who initially declined to participate but subsequently agreed differed from those who initially agreed on a number of demographic and reproductive characteristics, and estimates of ectopic pregnancy risk associated with induced abortion and tubal sterilization changed slightly with the inclusion of initial nonparticipants. We conclude that use of a card-back system of subject contact yields a low level of positive response among reproductive-aged women and that many initial nonparticipants can be converted into participants by personal contact and the offer of compensation.