IMPORTANCE OF PARTICIPATION RATE IN SAMPLING OF DATA IN POPULATION-BASED STUDIES, WITH SPECIAL REFERENCE TO BONE MASS IN SWEDEN

Objective - To study the effects of participation rate in sampling on ''normative'' bone mass data. Design - This was a comparison between t wo randomly selected samples from the same population. The participati on rates in the two samples were 61.9% and 83.6%. Measurements were ma de of bone mass at different skeletal sites and of muscle strength, as well as an assessment of physical activity. Setting - Malmo, Sweden. Subjects - There were 230 subjects (117 men, 113 women), aged 21 to 42 years. Results - Many subjects participated in both studies (163). Th ose who took part only in the study with the higher participation rate (67) almost invariably had higher values for bone mass density at the sites measured (up to 7.6% for men) than participants in the study wi th the lower participation rate. No differences in muscle strength wer e recorded. Conclusion - A high degree of compliance is important to a chieve a reliable result in determining normal values in population ba sed studies.