Liver transplantation after paracetamol overdose - Europe PMC

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not survival is improved when surgery is done by specialists because, as ... postoperative morbidity and mortality and ultimate survival. BMJ 1991;302:1501-5.
made in table VII (that is, 13 surgeons by three types of operations and all operations together). Thirdly, no data are given to show whether or not survival is improved when surgery is done by specialists because, as the authors say, none of the surgeons specialised in this type of surgery. Furthermore, the postoperative mortality and complication rates for the four consultants with over 40% oftheir operations performed by surgeons in training were no worse than those for the other surgeons. Fourthly, comparing the hazard rates in the 10 years after surgery ignores the possibility that factors influencing postoperative mortality may well differ from those influencing longer term mortality. For example, postoperative mortality may be related to the technical skill of the surgeon, but longer term mortality might be related more to the surgeon's choice of procedure influenced by the patients' likely prognosis. Reporting large variability based on relatively small numbers resembles the situation on referral rates of general practitioners some time ago. Such studies had reported 20-fold variation in rates. Concern about this forms part of the government's justification for NHS reforms.' These studies were, however, based on small numbers of referrals and much of the variability could be attributed to random variation.4 Later studies involving larger numbers of referrals found significant but much smaller variations in referral rates.4 The paper by Messrs McArdle and Hole raises the important issue of significant variation in patients' outcome among surgeons. In our opinion there is insufficient adequate data and statistical back up to justify their conclusions. Further studies involving many more patients are required. VALERIE SEAGROATT SARAH HARRISON Unit of Clinical Epidemiology, Department of Public Health and Primary Care,

University of Oxford, Oxford OX3 7LF 1 McArdle CS, Hole D. Impact of variability among surgeons on postoperative morbidity and mortality and ultimate survival. BMJ 1991;302:1501-5. (22 June.) 2 Armitage P, Berry G. Statistic methods in medical research. Oxford: Blackwell Scientific, 1987:205. 3 Secretaries of State for Health, Wales, Northern Ireland, and Scotland. Working for patients. London: HMSO, 1989:3. (Cm 555.) 4 Moore AT, Roland MO. How much variation in referral rates among general practitioners is due to chance? BMJ 1989;298: 500-2.

AUTHORS' REPLY, -Mr W P Soutter was concerned about the value of audit. ' There has been considerable speculation in the media on the differences in outcome after treatment at different institutions and by different clinicians. We are concerned that the results of audit, uncorrected for variations in patient population and stage of disease, would be used as a basis for decision making by nonclinicians. We believe that we have shown how outcome, in this case after colorectal surgery for cancer, can be adjusted for known risk factors. With regard to Ms Seagroatt and Dr Harrison's questions about our statistical analysis, the logic adopted in our overall assessment of our results has been to limit the number of tests carried out to those data where statistical power is greatest and the data have been adjusted for known predictive factors (table VII). Considering the data for all patients, 13 tests of significance have been undertaken. Of these, one produces a probability value of