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LETTERS: G H Hall Authors may have underestimated number of young doctors still working in NHS BMJ 1999; 318: 1486 [Full text]

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Researchers got it right in estimating numbers of doctors lost from the NHS

Trevor Lambert, Michael Goldacre   (17 June 1999)

Researchers got it right in estimating numbers of doctors lost from the NHS 17 June 1999
Trevor Lambert, Statistician and Study Co-ordinator UK Medical Careers Research Group, Oxford University, Michael Goldacre Send response to journal: Re: Researchers got it right in estimating numbers of doctors lost from the NHS	Dr G H Hall (Letters, 29 May) questions the independence of the two methods we used to identify doctors working in the NHS and therefore questions the results obtained by our use of capture-recapture analysis (ref 1). He assumes that both methods depend on doctors' propensity to respond to enquiries. They do not. We identified doctors working in the NHS using two fundamentally different approaches. In both cases, the starting point was the nominal list of all doctors who qualified in Great Britain in 1988. The first approach used Medical Careers Research Group (MCRG) questionnaires sent to each qualifier regardless of where they were by 1995 (the year of the survey). The information obtained about doctors' employment in the NHS depended on doctors' responses. The second approach used the Department of Health's records, analysed by the Department for the same doctors at the same point in time. These records are based on information supplied to the Department by all NHS Trusts, generally using their payroll and personnel records information is not based on any enquiry to doctors, but on whether the Trust held an NHS contract for the doctor at the relevant time. It is the combination of results from these two independent methods which gives strength to our figure of an 83% participation rate in the NHS. Even if the two methods were not statistically independent, Dr Hall's point is flawed. He assumes that doctors identified as working in the NHS by one method would be more likely to be identified as working in the NHS by the other method. If true, this would reduce the estimated total number working in the NHS rather than increase it. In calculating the capture-recapture estimates, the higher the level of overlap between those identified by the two methods, the smaller the estimated additional number not identified by either method. Thus the real participation rate would be a little lower, not higher, than that with which Dr Hall takes issue. Yours sincerely Trevor Lambert Dr Michael Goldacre 1 Lambert TW, Goldacre MJ. Career destinations seven years on among doctors who qualified in the United Kingdom in 1988: postal questionnaires survey. BMJ 1998:317:1429-31.