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OBJECTIVE: To determine whether the way in which information on benefits and harms of long-term hormone replacement therapy (HRT) is presented influences family physicians' intentions to prescribe this treatment.
DESIGN: Family physicians were randomized to receive information on treatment outcomes expressed in relative terms, or as the number needing to be treated (NNT) with HRT to prevent or cause an event. A control group received no information.
PARTICIPANTS: Family physicians practicing in the Hunter Valley, New South Wales, Australia.
INTERVENTION: Estimates of the impact of long-term HRT on risk of coronary events, hip fractures, and breast cancer were summarized as relative (proportional) decreases or increases in risk, or as NNT.
MEASUREMENTS AND MAIN RESULTS: Intention to prescribe HRT for seven hypothetical patients was measured on Likert scales. Of 389 family physicians working in the Hunter Valley, 243 completed the baseline survey and 215 participated in the randomized trial. Baseline intention to prescribe varied across patients—it was highest in the presence of risk factors for hip fracture, but coexisting risk factors for breast cancer had a strong negative influence. Overall, a larger proportion of subjects receiving information expressed as NNT had reduced intentions, and a smaller proportion had increased intentions to prescribe HRT than those receiving the information expressed in relative terms, or the control group. However, the differences were small and only reached statistical significance for three hypothetical patients. Framing effects were minimal when the hypothetical patient had coexisting risk factors for breast cancer.
CONCLUSIONS: Information framing had some effect on family physicians' intentions to prescribe HRT, but the effects were smaller than those previously reported, and they were modified by the presence of serious potential adverse treatment effects.
In the medical literature, the results of clinical trials of preventive treatments are commonly reported in relative rather than absolute terms. For instance, the abstract of a paper by the West of Scotland Coronary Prevention Study Group on the effects of pravastatin in the primary prevention setting reports the study results only in relative terms—a 31% relative reduction in the frequency of definite coronary events with treatment.1 This proportional reduction is equivalent to an absolute risk reduction of 2.4% over 5 years. This represents a requirement to treat 42 middle-aged men for 5 years to prevent a single coronary event. This latter expression of the result is the number needing to be treated (NNT).
Although the relative risk has been shown to be the most stable estimate of a treatment effect across a series of studies, it does not adequately convey information about the magnitude of the benefits and harms of the intervention.2 The main disadvantage of reporting treatment effects as relative risk, or relative risk reduction when the treatment decreases risk of the event of interest, is that this statistic does not distinguish between groups of patients at different baseline risks.3–5 Thus, a constant relative risk can translate into a range of reductions in absolute risk, depending on the baseline (untreated) probability of the outcome of interest. If participants in a trial had a 10% chance of dying, and this was halved by treatment (50% relative reduction in risk), the absolute reduction in risk would be 5%, and 20 such individuals would have to be treated to avoid 1 death. In contrast, the same relative reduction in risk in a population with a baseline mortality of 1% is equivalent to an absolute risk reduction of 0.5%, and 200 would have to be treated to avoid a death.
There is evidence to suggest that the way information is presented (information framing) can influence perceptions about the worth of a treatment.6–12 This is most important when long-term preventive treatment is being offered to subjects at low risk of disease outcomes. Enthusiasm for prescribing appears to be higher when information on the treatment benefits is presented as relative risks than when the same information is presented as reductions in absolute risk,4 or as the NNT in order to prevent a harmful outcome.5,7,8
The management of hyperlipidemia has been the subject of most of the published studies of the effects of information framing on doctors' prescribing intentions.4,5,8,9 In these studies, the clinical context was kept simple. There was no attempt to replicate the complexity of “real world” decision making.
In the present study, we have investigated the effect of information framing on enthusiasm for prescribing long-term hormone replacement therapy (HRT). This study differed from most published studies by asking participants to consider simultaneously the benefits and harms of therapy in response to different scenarios. We hypothesized that physicians who received information regarding the putative benefits of long-term HRT (reduced rates of hip fractures and myocardial infarction) expressed in terms of relative risks would report a stronger intention to prescribe than those who received information expressed in the form of NNT. We were interested in the extent to which framing effects varied across different clinical scenarios, particularly when physicians were asked to weigh both benefits and potential harms of treatment when making their recommendations.
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This study confirms previous findings that physicians view interventions in a more positive way when information on their benefits is presented in relative rather than in absolute terms. However, the overall effect of information framing was smaller than has been observed in other studies,6,7,9,10 and was inconsistent across different clinical scenarios.
The study differs in a number of respects from previous work. First, we included a control group who received no information but were asked to respond to the scenarios on two occasions. This group tended to increase their intention to prescribe during the study, as did the group who received the information framed as change in relative risk. The change in intention to prescribe in the control group may be an effect of involvement in the study or may be due to other activities focusing on use of HRT that were occurring over the study period. This clearly illustrates the need for a control group. For scenarios describing women at risk of myocardial infarction, there were no differences between the control and relative risk groups, and the majority of the relative risk group did not change their prescribing intentions for scenarios describing risk of hip fracture. This possibly indicates a conditioning effect of repeated exposure to claims regarding the benefits of HRT for hip fracture being expressed in relative terms. Most coverage of the issue in the lay and medical press in Australia seems to have taken this form. In contrast, physicians may have been less aware of the evidence of a claimed beneficial effect of estrogens on the cardiovascular system, as their baseline intention to treat was less than for prevention of osteoporosis. This may explain the increased intention to prescribe to the women described as being at high risk of myocardial infarction after exposure to the information expressed in relative terms. In contrast, the doctors who received the estimates framed as NNT displayed lower enthusiasm for prescribing than the control group across all scenarios, and these differences were statistically significant for the scenarios describing women at moderate or high risk of hip fracture.
Another difference between this and most other studies was that we asked participants to consider simultaneously the benefits and potential harms of therapy when making a decision to prescribe. With the two scenarios that described women at moderate to high risk of developing breast cancer, the impact of information framing was small and could have occurred by chance. It was noticeable that intention to prescribe to women at high risk of breast cancer (scenarios 6 and 7) increased in only small proportions of respondents—the majority becoming less likely to prescribe, or not changing their intentions. This suggests that doctors are “risk averse” when they are asked to consider the adverse consequences of their actions, and in such situations the way the information is framed may have little impact.
We have recently completed a systematic review of the literature on the importance of framing in relative rather than absolute terms.21 The design of many of the studies has been suboptimal. All have involved some element of within-subject comparison. Consequently, the response to one information frame may be conditioned by recent exposure to the other frame. It is uncertain what effect this will have had, but our opinion is that it may have exaggerated responses and may have led to an overestimate of the true impact of information framing. The lack of control groups who received no intervention is another concern. In our trial, we measured changes in intention scores within a prospective parallel group design. The pattern of change in the control group was similar to that in the relative risk group in several of the scenarios. Previous studies have not determined the baseline intention to prescribe. Although they were able to conclude that the rating of effectiveness, or likelihood of prescribing, was greater when information was presented in relative rather than in absolute terms, it is unclear whether this was because of an increase in intention in one group, a reduction in the other, or a combination of these trends. The present study suggests that the main effect is a reduction in intention when information is presented in absolute terms and baseline event rates are low.
Criticisms can be made of the wording used to present information in this and other studies. Specifically, the word “relative” has been used inconsistently.6,8–12 In pilot testing our information package, we found confusion regarding the meaning of the term “relative” in the context of the study and dropped it. We preferred alternative wording that implied a comparison of the risk in the treated group with a nontreated group (see Appendix B). Some participants may have concluded that the relative risk reduction quoted in the information package was a large absolute reduction in risk, and such a misinterpretation may have affected other studies of information framing.6,8–12
Information-framing studies have often failed to control for time preference, and this is also a criticism of the present study.7–10,12 The tendency has been to mention the duration of therapy that is necessary to achieve the absolute benefit, but not to mention it when describing the benefits in relative terms. Consequently, participants may have concluded that the relative benefit was immediate, while the absolute benefit was deferred. These factors could contribute to the negative impact of absolute risk presentations.
In conclusion, the way information is framed has an impact on intention to prescribe long-term HRT. However, the magnitude of the effects of information framing appears to be less than that reported in previous studies. In part, this may be a consequence of the design of some of these studies, but it is also likely to be due to the more complex clinical situations that we presented to the participants in this study. In particular, the effects of information framing on the use of preventive therapies may be small when doctors are asked to contemplate the harmful effects of their interventions.
The authors are indebted to the many general practitioners in the Hunter Valley NSW who participated in this project, which was funded by grants from the Pharmaceutical Education Program and the National Health and Medical Research Council, Commonwealth Department of Health and Aged Care, Canberra, ACT, Australia.