Variations in health authority performance cannot be explained away by variations in social and economic conditions, a King's Fund study has concluded.

In a report following work to compile a single indicator of performance for the NHS for Channel 4 earlier this year, authors John Appleby and Jo-Ann Mulligan say HAs responded to their rankings by arguing they reflected underlying socio-economic conditions.

But the authors argue that HAs are already funded to help iron out such differences. They also argue that such factors should not be regarded as 'confounding variables' since policies can be devised to address them. They argue that these factors account for only about 40 per cent of the variation shown up by the indicator chosen, a composite of six measures weighted according to the importance given to them by 2,000 members of the public.

The rest of the differences, they argue, could be due to other factors affecting health, but also to NHS performance and access to NHS services.

Mr Appleby said the results suggested that although 'upstream' measures such as improving housing and tackling pollution were 'undoubtedly necessary', the NHS also had a role to play in improving health.

On the other hand, he warned they also showed that the government's national plan for the NHS would not succeed in reducing health variations unless ministers also looked at the whole range of government activity affecting health inequalities.

How Well is the NHS Performing? The King's Fund bookshop, 020-7307 2591.£6.99.