Regional differences in outcome from subarachnoid haemorrhage

Background. Surgeons are increasingly placed under pressure to accept publication of their results and to abide by recommendations to change practice which others derive. Considerable concern exists about misinterpretation of such data. The issue is well illustrated by this study. Method. Data on outcome following treatment for subarachnoid haemorrhage were prospectively collected from 1993-1998 in two centres in the British Isles: Newcastle and Nottingham. Findings. Initial examination of this data suggest a substantial difference in the performance favouring Nottingham over Newcastle. The odds of a poor outcome was 1:1.86 in Newcastle compared with 1:4.26 in Nottingham giving an odds ratio of 2.3 in favour of Nottingham and this difference was highly significant with p < 0.00001. On a more detailed examination taking account of confounding variables, this difference disappeared entirely. Newcastle was able to operate a less selective admissions policy than Nottingham because of the deficiency of beds at the latter unit. A summary of these results has been published elsewhere. Interpretation. These results illustrate the dangers of applying statistical tools developed for simpler situations such as industrial process control to complex medical problems. We conclude that comprehensive and accurate data on all factors likely to influence the outcome for a particular treatment should be collected as an absolute prerequisite to any judgments being made on apparent statistical differences between the performances of differing units.