Data on children looked after by local authorities in England is collected via annual returns known as the SSDA903 return from English local authorities. Data are collected at individual child level on those who are in care at 31 March each year, those who start or cease to be looked after including those adopted from care during the year ending 31 March, and for those who have recently left care, information as to their activity and accommodation on their 19th birthday is also collected. Characteristics of these children are collected including date of birth, gender, ethnicity, category of need, type of placement and legal status.
The child level records are linked together across years to form a longitudinal database and each year, local authorities are able to amend data they have returned for previous years to reflect any changes or new information.
The SSDA903 data collection has existed in its current form since 2004. Prior to this it was made up of a series of separate returns, and from 1998-2003 there was a one-third sample collection as well as an aggregate return.