Theories of change: what works in improving health in mid-life?

The need to promote healthy active ageing in order to offset the impact of an ageing population on national resources and ensure a high quality of life in older age is well recognized. In 2001, the English Department of Health established a national pre-retirement health initiative involving the development of eight pilot projects. A national evaluation using a 'theories of change' approach embedded within a realistic evaluation design was commissioned to draw out the lessons from across the projects.