Annual performance ratings are being beefed up for some NHS sectors to make fairer comparisons possible across the service.

The Healthcare Commission has tailored its yearly performance ratings system for 2008-09, to combat criticism that some trusts face a far more rigorous test than others.

Mental health trusts and ambulance trusts have tougher indicators and primary care trusts will be assessed on their commissioning and provider functions.

Healthcare Commission chief executive Anna Walker said: "During consultation we were told the assessment, for mental health trusts for example, needed to be more stretching and what we were proposing wasn't radical enough."

New indicators for mental health trusts cover levels of follow-up care within seven days of discharge, services for children and adolescents and data collection.

Ambulance trusts will now be assessed on their management of conditions, including asthma and cardiac arrest.

Assessments of PCT commissioning are likely to draw on world class commissioning indicators.

Ms Walker said: "PCTs are extremely concerned that they might face a double jeopardy through world class commissioning and the annual health check.

"We're still making up our minds about that, but we hope to take the world class commissioning framework and use it for our assessment processes."

Ratings for all trusts will take into account patients' experiences through the national patient survey, patient forums and overview and scrutiny committees.