The government's star ratings system is misleading patients over which hospitals are performing best, according to research published on Friday.

Researchers from the Intensive Care National Audit and Research Centre and the London School of Hygiene and Tropical Medicine compared data from 102 NHS trusts across England.

Writing in the British Medical Journal, they concluded that the hospital's star rating did not accurately reflect the standard of adult critical care provided.

In addition, the researchers argued that when assessing a trust's performance, officials rely too much on crude data, such as mortality rates, without considering the circumstances surrounding that particular hospital, such as the types of patients that it treats.

"Patients do just as well in a trust with no stars as they do in one with three stars," said the report.

"Crude mortality data are misleading because they ignore the fact that higher-rated trusts tend to be teaching institutions with patients who are less severely ill on admission to critical care units."

"Hospitals are complex organisations containing many services; performance across a hospital will not be uniform - a poorly rated hospital may contain some excellent services, and vice versa," it added.

The Commission for Health Improvement defended the rating system.

"We have always said that star ratings are far from perfect and we have always been committed to improving them," said a spokesman.

"This report only focuses on intensive care and we do look at more than just outcome indicators.

"We accept there is a lack of good quality data and we are looking at getting hold of that data."

But shadow secretary of state for health and education Tim Yeo said the star ratings should be scrapped.

"This report further undermines the credibility of the Department of Health's ratings system," he said.

"The system is ludicrous and should be scrapped. The ratings bear no relation to the quality of care that patients are receiving.

"Nothing illustrates this point more vividly than the unanswered questions surrounding why South Durham Trust, in the prime minister's constituency, was upgraded from two to three stars in July 2002 after the involvement of the private office of the then secretary of state for health and with the knowledge of Number 10.

"The government must start to put patients first and stop using the NHS for their own political ends."