The English Longitudinal Study of Ageing (ELSA) is a study of people aged 50 and over and their younger partners, living in private households in England. The sample was drawn from households that had previously responded to the Health Survey for England (HSE) in 1998, 1999 or 2001. The data collection for the ELSA sample at HSE is known as "ELSA Wave 0". (Households from HSE 2000 have been sampled for piloting each wave of ELSA.)

The ELSA Wave 0 sample will form the basis for all subsequent waves of the study,although a refreshment sample of younger HSE sample members has been added at Wave 3. This sample has been added because, as the study progresses all the respondents get older, so we need to replace the youngest people as they are no longer represented. This new sample of respondents, aged 50 to 53 (and their older/younger partners), was drawn from responding households at HSE 2001, 2002, 2003 and 2004.

The Wave 0 data for these respondents will be deposited in the archive after ELSA Wave 3 has been completed. Further refreshment samples may also be added at future waves