The Good Hospital Guide, published by Dr Foster Intelligence, ranks hospital performance based on standardised mortality rates.
But research from the University of Birmingham, commissioned by West Midlands SHA, found that those rates are a poor indicator of the quality of care provided.
As much as 30 per cent of their variation is explained by differences in the way hospitals record diagnoses, it found.
Low mortality rates could often be attributed to the availability of end-of-life care outside hospital, in settings such as hospices.
The DoH published its own mortality rates for four types of operation last month.
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