Hum. Reprod. Advance Access originally published online on September 23, 2004
Human Reproduction 2004 19(12):2838-2844; doi:10.1093/humrep/deh521
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Selection bias in semen studies due to self-selection of volunteers
1 INSERM (National Institute For Health and Medical Research) U569 IFR69, 94276 Le Kremlin-Bicêtre, 2 Service de Biologie de la Reproduction-CECOS, Hôpital Cochin, EA 1752 Université Paris 5, 75014 Paris, 3 CECOS Midi-Pyrénées, Research Group ‘Human Fertility’ (E1 3694), 4 Centre de Stérilité Masculine, Service d'Urologie Andrologie, Hôpital Paule de Viguier, 31059 Toulouse, 5 Service de Biologie de la Reproduction-CECOS, Hôpital de l'Hôtel-Dieu, 35000 Rennes and 6 Département de Médecine et Biologie de la Reproduction, Faculté de Médecine-CECOS, 69373 Lyon, France
7 To whom correspondence should be addressed at: INSERM U569, 82 rue du Général Leclerc, 94276 Le Kremlin-Bicêtre cedex, France. Email: muller{at}vjf.inserm.fr
BACKGROUND: Reports of a secular decrease in semen quality remain controversial, particularly due to the possibility of selection bias. We aimed to describe the potential bias due to self-selection of volunteers in semen studies involving fecund men. METHODS: Using data from the French multicentre study REPRHOM, we compared the characteristics of the partners of pregnant women for three levels of participation: completion of a refusal questionnaire (n=698), agreement to complete the study questionnaires only (n=676) and agreement to complete the study questionnaires and give a semen sample (n=331, 13% of the subjects approached). RESULTS: Poorly educated men refused more often to participate than highly educated men. Semen providers were more likely to have experienced unfavourable pregnancy outcomes (odds ratio 1.68, 95% confidence interval 1.14–2.49) compared with participants completing the questionnaires only. Time to pregnancy was similar for all participants. CONCLUSIONS: This study demonstrates the existence of selection bias in semen studies associated with fertility and socio-demographic characteristics of men. The results of semen analysis for this population sample cannot be extrapolated to the whole population from which the volunteers originate. More information is required on who participates, and participation rates should be reported in semen studies to make it possible to interpret the results correctly.
Key words: bias (epidemiology)/fecundity/participation/selection bias/semen studies
This article is a corrected version of that originally published. In the previous version, some corrections requested by the authors at proof stage were not incorporated. The publisher would like to apologise for this error.
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