Prescribing by numbers

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Editor, – It was interesting to see an article on the number needed to treat (NNT) (Aust Prescr 2000;23:38). NNT is better than looking at relative risk reductions but NNT still does not always give you a feel for the relevance of an intervention.

I believe clinical decision-making needs to consider two numbers. These are the paired absolute incidences.

X = Event rate control (the outcome with placebo, or the outcome if you do nothing)
Y = Event rate active (the outcome with treatment)

Consider a room full of 100 people with a clinical problem. Put it to them, 'Do nothing and the event will happen to X of you, and if all of you take the pill it will happen to Y of you.' Using the Helsinki Heart study as quoted in the article, how would 100 men respond if told 'Take gemfibrozil for five years and 4.1 of you will have an event, do nothing and 2.7 of you will have an event'? I suspect many would say why bother with treatment, but some would say OK.

Clinical decision-making needs to be made in the context of real people. Other comorbidity, patient attitude, patient expectations, the psychological burden of disease label, adverse effects, secondary costs (for example, more visits to the doctor) all need consideration. I believe that by looking at the two numbers (X and Y) I can get a better feel for the relevance of an intervention, and also inform my patients about 'doing something' versus 'doing nothing'.

I believe the treatment of risk and risk factors is greatly overrated, and that many are treated for risk without a genuine consideration of how much of a difference it could make for the individual. As the surgeons learn to withhold the knife, I believe we should learn to hold back the drug treatment of risk factors, not because there is no evidence, but because in the bigger picture it is irrelevant to the patient - this will be facilitated by looking at the X and Y numbers.

Paul Neeskens
General Practitioner
Hervey Bay, Qld