What method of contact works best for recruiting participants in a study: lessons for health care researchers?

Objectives: to assess the various recruitment strategies used by medical researchers and their response rates. methods: the observational study, part of a larger retrospective cohort, was done at the aga khan university hospital, karachi, pakistan, from may 2008-december 2010, covering a period from 1999 to 2005. we used a multi-mode contact approach for including participants in the study. this comprised an invitational letter that described the study sent along with a mail-back, postage-paid envelope and multiple phone calls for recruitment of participants. the response to each mode was noted and described as frequency and percentage. results: there were 1335 participants eligible for recruitment in the study. of them, 1247 (93.4%) were sent mail- outs to which only 84 (6.7%) responded. besides, 1133 participants,whose phone numbers were available, were called. overall, the number of people that we were able to contact was low. the response to postage paid mail was very poor whereas the majority of participants were contacted via phone calls. out of such participants, 257 (19.25%) agreed to participate at the very first call and our results suggest that more than three calls made very little contribution to the consent rate. conclusion: recruiting subjects from contact information available in the medical records may not be the best method. multiple and innovative approaches are required for approaching potential participants and requesting them to participate in a study.