NorLAG is based on a nationally representative and stratified sample of older adults. Statistics Norway has been responsible for the sampling procedure and data collection in all three waves. Participants in the first wave (NorLAG1) were sampled from the population born 1922–1962 (aged 40– 79 years at the time of interview), living in 30 municipalities/townships across Norway. Within each municipality/township, the sample was stratified according to gender and age. Data for NorLAG1 were collected during 2002 and 2003.
The second wave (NorLAG2) was conducted in 2007– 2008. The sampling frame for NorLAG2 included the gross sample of NorLAG1 and a large refreshment sample covering the whole country, including also respondents born 1962–1966 (aged 40–44 at the time of interview). The sample was stratified according to gender, age, geographical region and centrality of residential municipality (most central – least central).
The third wave of NorLAG (NorLAG 3) was conducted in 2017 and included all living participants born between 1922 and 1966 who had responded to NorLAG1 and/or NorLAG2. In 2017, the youngest respondents were 50 years and the oldest 94 years of age.
NorLAG uses two different interview modes. All participants are contacted for a computer-assisted telephone interview (CATI). After completion of the CATI, respondents received a self-completion questionnaire. In NorLAG3 participants could choose between a web-based and a postal questionnaire. Response rates for the three consecutive waves are 67, 61 and 68 %, of which approximately 75 % returned the self-completion part.
NorLAG data collections have been funded by the Research Council of Norway, four ministries (Health and Care, Work and Social Affairs, Children and Families, Local Government and Modernisation), Directorate of Health, The State Housing Bank, Statistics Norway and NOVA. NorLAG data are made available for research purposes through the Infrastructure projects funded by the Research Council of Norway ACCESS Life Course (prosjekt no. 195403) and ACCESS Upgrade (project no. 269920), a consortium between NOVA and NSD.