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The older Finnish Twin Cohort study started in 1975, with follow-up questionnaires in 1981 and 1990. There has been registry-based follow-up, and numerous clinical and intensive studies on smaller numbers of twin pairs as described earlier (Kaprio & Koskenvuo, 2002). For the past 5 years, our focus has been on registry-based follow-up, reporting on studies in which data collection has been completed, and participation in multicentre studies.
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