The Mediterranean Osteoporosis Study (MEDOS): theoretical and practical issues of a major international project on hip fracture epidemiology.

The Mediterranean Osteoporosis Study (MEDOS), a multicentre study on incidence, risk factors, and means of prevention of hip fracture in the Mediterranean region, started in 1986 and involved 14 centres, in Portugal, Spain, France, Italy, Greece, and Turkey. The project comprised three parts: a) a collection of existing register data on hip fracture occurrence from the 31 European ministries of health; b) a study of hip fracture incidence in the defined areas of the participating centres in the Mediterranean countries in age groups above 50 years; c) a case-control study comparing 8,185 individuals (2,816 cases and 5,369 controls; two controls per case). The structure of the project and its development is described. Methodological issues involving questions of reliability and validity are discussed. A number of measures were taken in order to obtain a high quality study, e.g., retranslations of the questionnaire of the case-control study, a separate reliability study of the interviewers' performance and uniformity, and a systematic tracing and estimation of the impact of errors in the data processing procedure. The complexity of the management process and the importance of effective communication on methodological issues are underlined.