1. Armitage P (1974) Statistical methods in medical research, 4th printing. Blackwell, Oxford
2. Banks MH, Glegg CW, Jackson PR, Kamp NJ, Stafford EM, Wall TD (1980) The use of the general health questionnaire as an indicator of mental health in occupational studies. J Occup Psychol 53: 187–194
3. Breslow NE, Day NE (1980) Statistical methods in cancer research, vol 1. The analysis of case-control studies. IARC Scientific Publications no 32, Lyon
4. Goldberg DP, Hillier VF (1979) A scaled version of the general health questionnaire. Psychol Med 9: 139–145
5. Hollnagel H (1985) 40-âriges helbred (Health status of 40-year-olds). Thesis, Institute of General Practice, Kobenhavns Universitet, Kobenhavn