Design, material and methods in the NORA study. Nordic Research on Ageing.

This paper describes the research design of the NORA (Nordic Research on Ageing) study carried out in three Nordic localities. Response and participation rates in the baseline (age 75) and follow-up (age 80) studies are shown for each locality; in addition, the number of dead and censored cases are presented. In Göteborg, 450 persons were randomly sampled for invitation to the baseline study among all persons aged 75 years; in Glostrup, 571 persons aged 75 were selected, and in Jyväskylä all 388 persons aged 75 were selected. Baseline measurements were conducted in Jyväskylä and Glostrup in 1989, and in Göteborg in 1990. The participants were first interviewed at home, and afterwards went through tests and examinations in a standardized laboratory environment. The follow-up study was carried out five years after the baseline study. In Jyväskylä 92.9% (N=355), in Göteborg 82.5% (N=368), and in Glostrup 84.5% (N=480) of the eligible subjects took part in the baseline interview; corresponding figures for taking a test at the laboratory/clinic of the study center were 77.2% (N=295), 72.4% (N=323) and 72.4% (N=411). For the follow-up interview, those subjects who took part in the baseline interview were considered eligible. The participation rate was 93.6% (N=250) in Jyväskylä, 76.6% (N=226) in Göteborg, and 79.1% (N=277) in Glostrup. Corresponding figures for the tests at the study center were 71.5% (N=191), 71.9% (N=212) and 59.7% (N=209). The mortality rate was lowest in Göteborg (19.0%), and highest in Glostrup (27.2%). The data of the NORA study enables various types of descriptions and comparisons to be made across localities and measurement occasions.