Finntwin16

Finntwin16 is a family data collected as a twin follow-up study. Data collecting started between 1991 and 1995 when questionnaires were mailed to all Finnish twins born between 1974 and 1979 as well as to their parents. Twins were 16 years old at the time when first questionnaires were sent. Later questionnaires have been mailed when twins were 17, 18½ and 23 to 27 years old. Finnish Population Register Centre provided twins' contact information for the study.

The study began by mailing an invitation to twins, so that correct address and possible partipication refusals could be defined. Twins and their parents got the questionnaires few weeks after their 16th birthday. This gave us the possibility to standardize twins' age rather precisely. Twins were approximately 16 years and two months old as they filled up the questionnaires. It was very important to have the twins answering the questionnaire at same age, because use of alcohol changes rapidly at that age. 17-year-old questionnaires were also sent in the same way described above. 18-year-old questionnaires have been mailed when twins were approximately 18 and half years old. Both Finnish and Swedish speaking participants could answer the questionnaires in their own language. Later the questionnaires have been also translated into English to documentate the study more precisely.

If the sent questionnaire wasn't given back, a reminder was sent. If we still couln't get a reply, we either tried to contact the twin by phone or mailed a new reminder. Small gifts with information about the results of the study have been sent to those who participated. Motivating twins is important in a long-term follow-up study to keep the participation procents as high as possible.

The 16-year-old questionnaire was given back by 5563 twins (2881 girls and 2682 boys), which is about 92 % of girls and 87 % of boys invited. 85 % of Swedish speaking twins invited participated the study. New questionnaires (as described above) were sent to those who participated in the 16-year-old questionnaire. Over 90 % of invited twins and their families participated in the follow-up study, in which last questionnaires were sent in 1998. In overall 87 % of girls and 76 % of boys took part in the whole study. 84 % of twins' fathers and 87 % of mothers participated. Mothers were approximately 46 years old and fathers were approximately 44 years old at the time questionnaired. 82 % of families lived together. Five families had two twin pairs.

In conclusion, the Finntwin16 dataset represents a rich longitudinal design and covers well the Finnish population.

Links

Many articles and doctoral theses have been published from this study. Below are a couple of samples: