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Framing

 

There has been research on the interpretation of numerical information and how that depends on the presentation of the information. Technically this is known as framing, and the effects of framing have been examined in a systematic review [1] of 12 studies published up to about 1998. Relative risk reduction or increase were outputs that viewed most positively by doctors, but formal meta-analysis was not possible. Some selected studies are examined below, but the review concluded that the effects of framing on clinical practice are unknown.

Purchasers and presentation

The importance of the way in which information is presented is emphasised by Fahey et al [2], who gave 182 health authority members results from a randomised trial on breast cancer screening and results from a systematic review on cardiac rehabilitation. The results were presented to them (Table 1) in four different ways:

Table 1: Presentation of results on mammography and cardiac rehabilitation

Information presentation
Manmmography
Cardiac rehabilitation
Relative risk reduction
34%
20%
Absolute risk reduction
0.06%
3%
Percent of event-free patients
99.82% vs 99.80%
84% vs 87%
Number needed to treat
1592
31

From the 140 questionnaires returned the willingness to fund either programme was influenced significantly by the way in which results were presented. Relative risk reduction produced significantly higher inclination to purchase, followed by NNT. Intriguingly only three respondents, "all non-executive members claiming no training in epidemiology" said that they realised that all four sets of data summarised the same results.

Doctors and presentation

It is not only members of health authorities who are susceptible to altered perceptions of effectiveness according to the way in which the results of studies are presented to them. Two studies have looked at the effects of presentation on decisions by doctors in teaching hospitals in Canada [3] and on GPs in Italy [4]. Both used data from the Helsinki heart study.

Hospital doctors

In the first of these studies, David Naylor and colleagues [3] compared clinicians' ratings of therapeutic effectiveness by looking at different end-points presented as percent reductions in relative risk, absolute risk, and numbers-needed-to-treat. The study was conducted using random allocation of questionnaires using relative data or absolute data, each with NNT, among doctors of various grades at Toronto teaching hospitals. They used an 11-point scale anchored at 'no effect' and running from -5 'harmful' to +5 "very effective".

Relative presentation consistently showed a tendency to higher scores - that is the intervention was interpreted as being more effective (Figure 1). Where data from a single end point, for any myocardial infarction, was examined, both relative and absolute comparison was scored consistently higher than NNT presentation of the same data. NNT reporting of the same information produced a reduction of about two points in the effectiveness scale, reducing the judgement from quite effective to one of only slight effect.

Figure 1: Scoring effectiveness on "any myocardial infarction" by method of presentation


General practitioners

This second study [4] presented information to 148 GPs using information from the trial as if it referred to five different drugs. The presentations were:-

For each statement about effects, the GPs were asked to mark a 10 cm line labelled "I would definitely not prescribe this drug" on the left and "I would definitely prescribe this drug" on the right. The statements were presented in random sequences. The results are shown in Figure 2. Presentation as relative risk reduction produced a very large tendency towards prescribing with a mean score of 7.7 out of 10. All other presentations produced scores of between about 2.5 and 3.5.

Figure 2: GPs willingness to prescribe scores, by method of presenting data


US and European physicians and pharmacists

A more recent study looked at US and European physicians and US pharmacists and examined data presentation related to their willingness to prescribe a drug [5]. The same information was presented in three different ways, and overwhelmingly respondents chose data presented as relative risk reduction as that most likely to make them prescribe (Figure 3).

But three distracter statements about life expectancy, cost and hospital admission rate also attracted significant attention as first-choice determinants, and about 40% of respondents preferred those over clinical trial results.

Figure 3: Choice of information for determining prescribing decision


Interestingly, determinants were slightly different for European physicians from US physicians. European physicians were much more influenced by NNT and absolute risk reduction (and cost and hospital admission), and they were much less influenced by relative risk reduction. Despite this, relative risk reduction remains a potent influence on decisions, as a UK study confirmed [6].

References

  1. P McGettigan et al. The effects of information framing on the practices of physicians. Journal of General Internal Medicine 1999 14: 633-642.
  2. T Fahey et al. Evidence-based purchasing: understanding results of clinical trials and systematic reviews. BMJ 1995 311: 1056-60.
  3. CD Naylor et al. Measured enthusiasm: does the method of reporting trial results alter perceptions of therapeutic effectiveness? Annals of Internal Medicine 1992 117: 916-21.
  4. M Bobbio et al. Completeness of reporting trial results: effect on physicians' willingness to prescribe. Lancet 1994 343: 1209-11.
  5. CR Lacy. Impact of presentation of research results on likelihood of prescribing medications to patients with left ventricular dysfunction. American Journal of Cardiology 2001 87: 203-207.
  6. M Cranney, T Walley. Same information, different decisions: the influence of evidence on the management of hypertension in the elderly. British Journal of General Practice 1996 46:661-3.