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CORRESPONDENCE-List of Contents ...... 259 OBITUARY ...... JU3.L..'...... 269 NEWS AND NOTES SUPPLEMENT fL-i"CCUREMENJT SECT4ON The Week . 274 URNT ,S Rte/ S Views ...... 271 From the Secretary: n as ...... 275 Epidemiology-Infectious hepatitis in a psychiatric hospital 272 Junior Hospital Staff: New circular on pay and conditions 276 Parliament-National Health Services Bill; Whooping- Incomes policy and the professions ...... 277 Professions write to Chancellor ...... 277 cough vaccine; Legislation on GMC ...... 272 GMC: Disciplinary Committee ...... 277 Medical News ...... 273 Extending role of clinical nurse-legal implications BMA Notices ...... 274 and training ...... 278

NO 6081 BRITISH MEDICAL JOURNAL 1977 VOLUME 2 209-278 ASTM CODEN: BMJOAE 2 (6081) 209-278 (1977) BRITISH MEDICAL ASSOCIATION TAVISTOCK SQUARE LONDON WC1H 9JR. WEEKLY. SECOND CLASS POSTAGE PAID AT NEW YORK NY BRITISH MEDICAL JOURNAL 23 JULY 1977 259 CORRESPONDENCE

When is significant not significant? Paget's disease of bone Rubella in early pregnancy

R Peto, MSC, and Sir Richard Doll, FRCP, J R Condon, MRCP ...... 263 J Nagington, MD ...... 266 Br Med J: first published as on 23 July 1977. Downloaded from FRS; G Silverman, MRCPSYCH ...... 259 Psychotropic drugs and road accidents Infantile acne Comparison of treatment with fast R P Snaith, FRCPSYCH, and others ...... 263 D Rowley-Jones, MRCP ...... 266 neutrons and photons Abdominal tuberculosis in Britain Treatment of mild hypertension Mary Catterall, FRCR, and others ...... 259 A M Smith, FRCS ...... 264 G H Hall, FRCP ...... 266 Relative activity of atenolol and metoprolol Campylobacter enteritis Cranial arteritis: atypical presentation M Brian Comerford, MB, and E M M N A Simmons, FRCPATH, and F J Gibbs, K D E Lawrey, MB ...... 266 Besterman, FRCP ...... 260 FIMLS ...... 264 Control of blood glucose in labour Poisoning with maprotiline and "Measles" in previously immunised K G M M Alberti, MRCPATH, and others.. 266 mianserin children Intravenous naftidrofuryl P Crome, MRCP, and Belinda Newman, BA. 260 W Ehrengut, MD ...... 264 D G MacLellan, MB ...... 267 Whooping-cough immunisation Bromocriptine and TRH-induced growth Diuretics and digoxin in myocardial G W A Dick, FRCPATH; J B P Stephenson, hormone release in anorexia nervosa infarction MRCP ...... 260 A D B Harrower, MRCP, and others ...... 264 R H Falk, MRCP ...... 267 Stress incontinence Survival of specialist societies Instant colour photography in E S Glen, FRCSED; S L R Stanton, FRCSED; dermatology R A Goodbody, FRCPATH ...... 264 P I Silverstone, MRCOG ...... 261 and A Y Finlay, MRCP, and others ...... 267 What did they say? Where did they come Phenylbutazone, oxyphenbutazone Prevention and health from? aplastic anaemia A W McIntosh, MD; Ruth M MacGillivray, L E Bottiger, MD ...... 265 P R Evans, FRCP ...... 262 MRCGP, and P R Brass, MB ...... 267 Shortage of anaesthetists Making better use of our nurses Disillusionment with area medical L J G Bourne, FFARCS; L Goodman, FRCSED.. 262 H W K Acheson, FRCGP ...... 265 advisory machinery Primary amenorrhoea Maintenance digoxin after an episode of P I Reed, FRCP, and G W Taylor, MRCGP.. 268 W P Black, FRCOG ...... 262 heart failure Work load of radiologists Prognosis of Henoch-Schonlein S J Warriington, MRCP, and N A J Hamer, M J Brindle, FRCP(C) ...... 268 nephritis in children FRCP ...... 265 The price of goodwill RLJ S Derham, MB ...... 262 Health visitors and child health G B S Roberts, FRCPATH ...... 268 Parallel aging of Achilles tendon and E J Morton, SRN ...... 265 Foreign graduates' entry to general coronary artery Chromium and diabetes practice T J Bassler, MD ...... 262 J Barbosa, MD ...... 266 Valerie S Neild, MRCP ...... 268 http://www.bmj.com/ Correspondents are urged to write briefly so that readers may be offered as wide making a serious error. This is a prevalent a selection of letters as possible. So many are being received that the omission error and so it has implications far beyond the of some is inevitable. Letters should be signed personally by all their authors. particular issue of the work of Professor Doll and Mr Peto. Professor Dudley claims that these two When is significant not significant? workers wish to have their statistical cake and also to eat it. This is just not so. Inferential SIR,-Professor Hugh Dudley (2 July, p 47) expensive error to conclude that failure to roll statistics are there to guide one's formation of is wrong to fear that if we dismiss a statistically double-six first time proved the dice to be belief but not to determine it, and it would be on 24 September 2021 by guest. Protected copyright. significant correlation as being due to chance unbiased!). It would be even more foolish, if only the naive person who would, before an we shall "destroy the logic of practical statis- 400 different pairs of dice were rolled and experiment, commit himself absolutely to tical inference." In fact the converse is true: double-six arose about a dozen times, to believing or not believing something as true or over-slavish adherence to rigid criteria of believe that all pairs which rolled double-six false, or due to chance or not due to chance, statistical significance is a fault as serious as the were loaded, although the analogy between simply because of a particular probability fault of ignoring the possibility that chance this and what Professor Dudley expects us to level. Such a person would be making himself alone has generated a certain effect. do is quite close. a slave to statistical methods rather than the In our recent paper (4 June, p 1433) we Conversely, if, for example, in our study appropriate way round-namely, allowing examined 400 different correlations between two radiologists died of cancers which were himself to use statistical methods as a servant particular occupations and particular causes of actually directly caused by their jobs, this to proper decision-making needs. Whether death and of course found a couple of dozen would probably not suffice to make the death one decides to believe that something is almost "statistically significant" associations. We rate statistically significantly high; so lack of certainly true or almost certainly false is suggested that some of these were genuine and statistical significance can, unfortunately, determined by many matters, not least ofwhich some the artefacts of chance; moreover, we often exist when there really is a true associa- is the importance of the findings in terms of suggested that some of the non-significant tion present. how these affect people and their welfare etc. positive associations were also genuine. In summary, we hope Professor Dudley In many cases, whatever the P value, an open Professor Dudley's suggestion that we achieves his expressed wish of immortality, mind is surely the necessary prerequisite to a should have accepted as true all associations but we hope that his "tenet .. . that given a good scientific worker and even more important that were statistically significant is unwise. certain probability level we will believe . to someone who has other peoples' welfare at Associations that are extremely (P < 0 001) will perish. stake. significant should very rarely be doubted, but RICHARD PETO G SILVERMAN moderate statistical significance (such as RICHARD DOLL St Bernard's Hospital, P < 0-05) often does arise as an artefact of Radcliffe Infirmary, Southall, Middx chance. For example, the probability of getting Oxford double-six when a pair of dice are rolled once only is one in 36, which is about 0 03. Thus if Comparison of treatment with fast we ever see someone roll double-six at his first SIR,-Professor Hugh Dudley (2 July, p 47) neutrons and photons throw of a particular pair of dice that is writes trenchantly against the statistical logic "statistically significant (P <005) evidence" of Sir Richard Doll and Mr Richard Peto SIR,-We are grateful to Dr W M Ross (9 July, that those dice are biased, but it would clearly (4 June, p 1433). I do not feel that Professor p 128) for drawing attention to the disadvantage be foolish to believe this on all such occasions Dudley deserves the annihilation which he that the majority of the patients treated with (and, in bad company, it might be quite an suggests is a possibility, but I think that he is photons in the MRC trial (25 June, p 1642)