The Avon Longitudinal Study of Parents and Children (ALSPAC)--study design and collaborative opportunities.

The Avon Longitudinal Study of Parents and Children (ALSPAC) is a population-based study designed to understand the ways in which the physical and social environment interact, over time, with the genotype to affect health, behaviour and development. This information about causal interactions in common diseases and disorders will provide the basis on which future preventive interventions can be tested, especially in regard to people with specific genotypes. Whilst ALSPAC builds on data and hypotheses generated by earlier general population cohorts, its design offers special advantages, the most important being: enrolment in early pregnancy; banking of DNA from the children and parents (permitting genetic transmission tests and transgenerational imprinting studies); diverse physical, psychological and environmental measures; one geographical base (permitting medical record and school linkage; environmental measures in the home, and clinics for direct examination); annual hands-on examinations of the full cohort since age 7. The 14 541 enrolled pregnancies (expected date of delivery 1 April 1991 to 31 December 1992) represented about 85% of the eligible population. The 13 971 children who were still alive at age 12 months have been followed principally by questionnaires completed by a parent. Twelve years on, questionnaires are still being sent out to 11 300 families. The average questionnaire response rate from mothers is 79%. From age 7, annual examinations of both 'physical' and 'psychological' aspects have also been conducted on the children (approximately 8000 attend each 'clinic'). The quality of the data has proved high in validation studies and is maintained by collaboration with experts in each specialist field. The high participation rate ensures a viable study well into the future.