Intended for healthcare professionals

Views & Reviews From the Frontline

The number needed not to treat

BMJ 2011; 342 doi: (Published 23 February 2011) Cite this as: BMJ 2011;342:d1197
  1. Des Spence, general practitioner, Glasgow
  1. destwo{at}

After finishing training for general practice I applied for an academic position for a year. I wrote a proposal on an observation I had made, that individual doctors generate much of their own workload. But as we say in Glasgow, “What’s for you won’t go by you,” and I wasn’t interviewed. My observation still holds true, however.

Doctors are aware of the NNT (number needed to treat), the number of patients who need to be treated for one to benefit from the intervention. (Remember that the NNT may be for many years of treatment, and when given per year the number may be far less impressive.) Fewer doctors are familiar with a more important concept, the NNNT (the number needed not to treat). The best example of an NNNT is the use of antibiotics for sore throat. If doctors don’t prescribe antibiotics, one in four patients will stop believing that antibiotics are effective, and a large percentage will not return with a sore throat again ( Extrapolated and compounded over time this clearly reduces pressure on medical appointments. And this observation is true of every self limiting illness.

This non-interventional effect is seen in almost all medical situations. Consider a doctor taking a blood test (often on the pretext of reassuring the patient but in reality to reassure the doctor). The patient tells everyone, “There is something wrong; they’re running further tests.” He or she waits anxiously to have the blood taken and then for the doctor to comment on the result. “Normal levels,” however, are but confidence intervals, so by definition some normal results lie outside this range. This then leads to further tests. Cue yet more anxious waiting, and, “The doctor must be really worried about me.” Should the “abnormality” persist, many patients are referred “just in case.” A simple routine blood test sets off a cascade of medical consumption, clogging general practice appointments and outpatient departments. This pattern is being repeated all the time all over the country. So, wide variation among doctors’ clinical practice leads to wide variation in their workload.

This is a fact. Use of healthcare and health seeking behaviour are directly affected by doctors’ behaviour. Doctors’ behaviour is linked directly to how they are paid. A private, fee for service system encourages medicalisation and consumption; a socialised system of capitation does not. This largely explains the huge cultural and international variations in the use of healthcare. The less doctors do, the lower our workload. Better still: the less we intervene, the less health anxiety we generate, and the more we promote self caring. There is more to healthcare than illness. A wider understanding of NNNTs would directly reduce our workload.


Cite this as: BMJ 2011;342:d1197

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