Six main clinical indicators apply to hospitals and 41 others assess the performance of health authorities.

Figures for the six indicators were established using more than 11 million hospital records.

The six indicators for hospitals show:

• Deaths in hospital within 30 days of emergency or planned surgery
• Deaths in hospital within 30 days of being admitted as an emergency with a broken hip
• Deaths in hospital within 30 days of a heart attack
• Patients readmitted to hospital as an emergency within 28 days of being discharged
• Stroke patients over 50 who return home within 56 days of admission
• Patients over 65 who return home within 28 days of admission with a broken hip

However, a poor score does not necessarily indicate the hospital is performing badly.

Not all the data is totally reliable - 17% of them were unusable.

Interpreting the figures

Headline figures fail to account for significant factors such as how ill a patient is when admitted.

This can lead to absurdities. For example, one cancer hospital performs no operations, but does insert catheters into terminally ill patients to relieve suffering.

This counts as surgery, so the hospital has one of the worst death rates following surgery - even though its patients will die anyway.

Comparisons can only be made between similar types of hospital in similar locations.

But even considering such factors when analysing the figures may not be enough - some trusts have already dismissed this year's figures as unreliable.

However, the Department of Health hopes the quality will improve over the years.