Children who are 'looked after' by the State are considered one of the most vulnerable groups in society. Being in State care is associated with poor social, educational and health outcomes. Exploring how to improve the system and better support children in care is key to improving these outcomes. When children and young people come to the attention of children's social services a significant amount of information about their care experience is routinely collected by local authorities. In Wales, routine data are captured in the 'Children Looked After' Census which is submitted annually to the Welsh Government.

The dataset LACB includes all care leavers who turned 19 years old between 1st April 2002 and 31st March 2016. There are no updates past March 2016. It is a subset of the primary Looked After Children in Wales (LACW) dataset. Other subsets include: Looked After Children Adoption (LACA); Looked After Children Care Leavers aged 16 and over (LACC); and Looked after Children - Education Qualifications (LACE). LACE was discontinued in 2016 (1999 - 2016) and included within LACW.

Due to the small number of looked after children with an Anonymised Linkage Field (ALF, 37%), a two-stage algorithm was developed. This algorithm utilises other datasets within SAIL to allocate children within the LACW ALF, increasing the overall ALF match rate to 61%. The improved ALF matches are available in the LAC ALF DERIVED table, part of the LACW dataset, and can be obtained by combined the SYSTEM_ID and LOCAL_AUTHORITY_CODE.