Participation bias in a randomised trial of screening for XXXX .

@entity1 @entity2
INTRODUCTION: Participation bias might affect the results and the representability of randomised controlled trials. We investigated the degree of socio-demographic and psychosocial participation bias in the Danish @entity2 Screening Trial (DLCST). METHODS: In DLCST the questionnaire COS-LC (Consequences of Screening in @entity2 ) was used to measure the psychosocial aspects of screening. To investigate a difference with a comparable representative sample from the Danish population, we sent out an inclusion questionnaire to 3999 Danes in the age from 50 to 70 years randomly selected from the Central National Register. Those who completed the inclusion questionnaire and met the inclusion criteria from DLCST received the COS-LC. Those who completed the COS-LC-and thus formed a population sample comparable to DLCST - were compared to the DLCST @entity1 on socio-demographics and psychosocial measures. RESULTS: Participation rates were high among the comparable population sample: 75.3% completed the inclusion questionnaire and 77.4% of those who were eligible completed the COS-LC. The analyses revealed differences between the DLCST @entity1 and the comparable population sample in the following socio-demographic aspects: social group, living alone, gender, age and geographical area. DLCST @entity1 reported less negative psychosocial aspects than the comparable population sample. CONCLUSION: The present study has shown substantial socio-demographic and psychosocial participation bias in DLCST.
