Since the year 2000, "choice-based lettings" (CBL) have been introduced to help ensure social housing was occupied speedily as tenants moved. This can still favour the local over the non-local prospective tenant. In a number of local authority areas, due to the shortage of council housing, three out of four properties may be designated for priority cases (those living in poor overcrowded conditions, with medical or welfare needs, or needing family support) or homeless applicants in order to meet the councils' legal obligations to rehouse people in need. The percentage of properties set aside for vulnerable groups will vary dependent on the demand for council housing in the area. All local authorities have a Housing Strategy to ensure that council houses are let fairly and fulfil the council's legal obligations; deal with people in need; and contribute to sustainability of housing estates, neighbourhood regeneration, and social inclusion.