A top UK hospital has become the first to publish all of its death rates.
Doctors fear mortality data could be misread
St George's Hospital, in south London, has put data for all its specialities online, taking into account risk factors such as age and diagnosis.
The information is published for 20 branches of medicine, but it is not broken down by individual doctor.
The only data currently available nationally is for heart surgeons, but doctors' leaders have expressed fears such data could be "misleading".
The Patients Association has been calling on all NHS hospitals to make available such data to help people exercise choice.
From the end of the year patients will be given the choice of up to five hospital for treatment.
The push for more openness also has roots in the Bristol Royal Infirmary scandal when surgeons were found to have continued carrying out heart operations on children even though they had higher than average death rates.
Heart surgeons are the most open as it is easier to measure outcomes but as yet national data is only broken down on a team by team basis.
However, a handful of hospitals - including St George's Hospital - have independently published individual information already.
St George's has said the latest data could not be broken down individually and could not be able to be compared to other hospitals if they published outcomes as there is no common way of assessing risk.
Hospital chief executive Peter Homa said: "We know that the more serious and complex the operation, the more the clinical safety, record and reputation of the hospital will be a factor for the patient, in consultation with their GP.
"By using carefully developed risk adjustment systems, in a format that is easy to understand, we can show our patients not only that we have high standards in patient safety, but also that they are steadily improving in the long term."
And he dismissed concerns people may have that the hospital was "oversimplifying" the data, saying they had got a good balance between publishing information that was easy to understand but took into account the complexities of medicine.
The death rates are published in the form of graphs on the hospital website at http://www.stgeorges.nhs.uk/mortalityintro.asp
Overall, more than 97% of people who go into the hospital come out alive, the data shows.
The British Medical Association said: "We believe it is important that patients have the information they need about doctors treating them.
"However, we are concerned that simply publishing crude figures will be misleading as they are dependent on many factors, importantly an individual's current health status will obviously impact on the success of their treatment."
Dr Gill Morgan, chief executive of the NHS Confederation, said: "In principle, we believe that the more information that is made available to patients, the better because that's the basis for patients making truly informed choices about their own care.
"However, crude figures alone are not enough - data needs to be adjusted to take into account the complexity of procedures being undertaken and the severity of patients' conditions because, if that's not done, then patients can end up making the wrong choices.
"We also strongly believe that raw mortality data must be accompanied by clear interpretation and explanation of what the data means."