BMJ 1995;311:1166 (28 October)

Letters

Authors' reply

EDITOR,--As D W Maclean and colleagues point out, we had hoped to isolate the effect of the helicopter and team from the effects of the major developments at the Royal London Hospital as well as assessing the effect of the helicopter emergency medical service as a whole. We were unable to do this with any reasonable power because too few control patients (those attended by an ambulance) who met our inclusion criteria were taken to the hospital during the 21 months of the study (n=40), not because too few patients were flown to the hospital by helicopter.

The power of the study is largely unaffected by the sampling strategy we used, and, with 336 patients attended by the helicopter and 466 ambulance patients, this was one of the largest studies of the effectiveness of emergency care provided by helicopter. It is disingenuous to mention that the central estimate for major . . . [Full text of this article]


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