A COMPARISON OF MORTALITY-RATES IN 3 PROSPECTIVE STUDIES FROM COPENHAGEN WITH MORTALITY-RATES IN THE CENTRAL PART OF THE CITY, AND THE ENTIRE COUNTRY

Valid generalizations of results from population-based epidemiological surveys requires knowledge about how representative the sample is. Th e Copenhagen Center for Prospective Population Studies have assessed m ortality on the basis of pooled data from three research programmes in the region of Copenhagen. In two of the studies, subjects were random ly selected, using the Danish Central Population Registry, within cert ain age groups and area-restricted sectors of the Greater Copenhagen. In the third study men employed in 14 companies participated. Particip ation rates were between 78 % and 87 % in the three programmes. Standa rdized mortality rates (SMR) were calculated in relation to mortality rates in the municipality of Copenhagen and in the whole country in th ree age groups and the two genders. SMR values in the whole sample inc luding non-participants were similar to rates for Copenhagen in the Co penhagen City Heart Study, whereas mortality rates in the Glostruy Pop ulation Studies were similar to rates for the whole country. The morta lity rates among participants were lower than in the whole sample, and differences existed in relation to region and selection criteria of t he cohorts. The Copenhagen Male Study, where only employed men were in cluded, showed the lowest mortality rates, and higher rates were found in the study from the central part of the City (the Copenhagen City H eart Study) compared to the study from the suburbs (the Glostrup Popul ation Studies). The difference between mortality rates in the cohorts and In Copenhagen City decreased with increasing age. The SMR converge d towards 1.00 with increasing observation time. In conlusion, high pa rticipation rates were found in all three studies, resulting in SMR va lues for participants only slightly lower than in the source populatio n :in the two randomly selected samples, but 30% lower values in the s ample of employed men. As mortality rates in the total samples includi ng non-participants were markedly higher than among the participants, generalizations of results for participants to the whole population sh ould be made with caution, especially during the first years of observ ation.