The chances of finding a good care home in some areas of England are close to impossible, an analysis suggests.
The review, by the Institute for Public Policy Research, found high concentrations of under-performing care homes in a number of local areas.
In a sixth of places over a third of beds for the elderly and disabled were in settings rated as not good enough.
Campaigners said this risked leaving families with no choice but to accept substandard homes for relatives.
In each local authority area the IPPR think tank mapped the proportion of care home places rated as inadequate or requiring improvement by the Care Quality Commission.
Overall, 23% of the 456,000 beds were in settings that fell into one of the two categories.
The best and the worst