A careful reading of the report should demonstrate that the pitfalls and mistakes that creep into many multicentre studies have been avoided. Sound findings can only be expected from good methodology. The most important single decision regarding the analysis of the data was the prior statement of 17 hypotheses which were to be tested statistically. With over 14 000 patients and with 210 items of information for each patient, there was scope for testing an immense number of combinations of variables. It would not be surprising if every twentieth such table showed a significant result at the 5% level. When reading published reports of research, it is always necessary to be alert for spurious claims which are consequences of such analysis. This is called data dredging. Admittedly, the number of findings that can be accepted as substantiated was limited by restricting the