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Decisions, decisions! QALYs etc

Occasionally it is instructive to see how evidence is used in making decisions in areas outside medicine. There are two external and two internal examples that Bandolier has found recently which made us think just how similar processes can be.

Validity and causation


Suppose you had data which showed that there was a highly significant inverse correlation between central bank independence and inflation: low inflation occurred in countries with highly independent central banks. The obvious decision, if you wanted low inflation, would be to create an independent central bank, and that has been a major tenet of economic thinking for a decade or so.

James Forder's trashing of this theory [1] originates in the fact that measures of central bank independence were so poor and inconsistent as to deny any relationship. We can't measure independence, so can't pontificate as to causation.

Health care decisions likewise require outcomes which make sense, and in whose measurements we can trust. Too often we see research papers or reviews whose only safe home is in the bin. Caveat lector : we have to be vigilant.

Feel the width


However much information we have, actually making a decision is often hard. Derek Pooley, faced with decision-making on renewable energy sources, used the simple guide of cost per tonne as a way of sharpening the mind [2]. This is a bit like a cost per QALY (the quality-adjusted life year) used in health care. Many people think it a crude measure, but since fine measures are unavailable (and may be impossible to get anyway), it has to serve. Ceri Phillips gives a good explanation of QALYs and costs [3], and some illustrative costs per QALY are shown in the Table.

Cost per QALY for healthcare interventions
Intervention £/QALY (1990 prices)
Neurosurgical intervention for head injury 240
GP advice to stop smoking 270
Neurosurgical intervention for subarachnoid haemorrhage 490
Antihypertensive treatment to prevent stroke (45-69 years) 940
Pacemaker implant 1,100
Hip replacement 1,180
CABG (left main vessel disease, severe angina) 2,090
Kidney transplant 4,710
Heart transplant 7,840
Home dialysis 17,260
Hospital dialysis 21,970


Quick and clean


Just how to use cost per QALY in health care decision-making is shown in a superb paper from Andrew Stevens and his colleagues from Wessex in 1995. This paper, which draws together all the themes in making decisions about new interventions, should be required reading. It provides guidance for ordering one's thoughts.



The paper also introduces Buxton's Law: 'it is always too early to evaluate a new technology until unfortunately suddenly it's too late'. It sets out seven stages needed for assessing technology (loaded towards the new, but highly applicable to existing technologies), and emphasises the importance both of analysis - drawing together information from a wide range of sources to bolster evidence from systematic review and meta-analysis - and costs - which have to be dealt with pragmatically.

They give us a simple-person's guide to making decisions based on levels of evidence and cost per QALY. Pragmatism is the name of the game. If, for instance, costs are lower than £3,000 per QALY, then the need for randomised trials may be relaxed. It is worth having a copy of this thoughtful and influential paper on your desk for re-reading at quiet moments.

References:

  1. J Forder. The case for an independent European central bank: a reassessment of evidence and sources. European Journal of Political Economy 1998 14: 53-71.
  2. D Pooley. Prospects for renewable energy sources in the United Kingdom. Proceedings of the Royal Society of Edinburgh 1987 92B: 73-89.
  3. C Phillips & G Thompson. What is a QALY? RPR Educational Series published by Hayward Medical plc: available as pdf file here , or in hard copy by calling 01638 751515
  4. A Stevens, D Colin-Jones, J Gabbay. Quick and Clean: authoritative health technology assessment for local health care contracting. Health Trends 1995; 27: 37-42.



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