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Table 1 Information relevant to sample retention and response rates for each cohort

From: Retaining young people in a longitudinal sexual health survey: a trial of strategies to maintain participation

Year and cohort (C) Wave Method Age Eligible start of Wave With-drawn Wrong address* Received quest. Got data (%) return rate of those still in study (%) return rate of original eligible sample
1996 C1 1 Classroom 13-14 4234 171 N/A1 4063 3812 93.8 90.0
1997 C2 1 Classroom 13-14 4196 165 N/A1 4031 3804 94.4 90.7
1998 C1 2 Classroom + postal2 15-16 4197 174* 147* 3876 2991 77.2 71.3
1999 C2 2 Classroom + postal2 15-16 4187 137* 176* 3874 2863 73.9 68.4
2000 C1 3 Postal 17-18 3876 127* 313* 3436 1116 32.5 26.4
2001 C2 3 Postal 17-18 3874 32* 282* 3560 1739 48.8 41.4
2002 C1 4 Mix3 19-20 3436 604* 32* 2800 1047 37.4 30.5
2003 C2 4 Postal 19-20 3560 598* 10* 2952 1439 48.7 40.4
  1. * When receiving a postal questionnaire, participants were told they could withdraw from the study by returning a blank questionnaire in the pre-paid envelope. Wrongly addressed questionnaires were returned by the postal service in their original envelopes. However, it is possible that new residents opened the envelope and then returned the blank questionnaire in the pre-paid envelope. Thus, there is a possibility of some of the 'withdrawn' numbers actually being due to a 'wrong address'.
  2. 1 The reason for N/A in this cell is that there was no possibility of a 'wrong address,' as all the questionnaires were completed in school classrooms, no pupils had left school and thus no pupils required a questionnaire to be posted out to them.
  3. 2In 1998, overall participation of 2991 (71% of Cohort 1), those in school setting 2517 (82%) and postal questionnaires 474 (41%). In 1999, overall participation of 2863 (68% of Cohort 2), those in school setting 2427 (79%) and postal questionnaires 436 (37%).
  4. 3The 'mix' was a choice of completing a web-based questionnaire, a telephone interview or a postal questionnaire.