Laypersons' understanding of relative risk reductions: Randomised cross-sectional study
BMC Medical Informatics and Decision Making
Laypersons' understanding of relative risk reductions: Randomised cross-sectional study
Lene Sorensen 1 2
Dorte Gyrd-Hansen 1
Ivar S Kristiansen 0 1
Jrgen Nexe 1
Jesper B Nielsen 1
0 Institute of Health Management and Health Economics, University of Oslo , Norway
1 Institute of Public Health, University of Southern Denmark , Odense , Denmark
2 Amgros I/S , Copenhagen , Denmark
Background: Despite increasing recognition of the importance of involving patients in decisions on preventive healthcare interventions, little is known about how well patients understand and utilise information provided on the relative benefits from these interventions. The aim of this study was to explore whether lay people can discriminate between preventive interventions when effectiveness is presented in terms of relative risk reduction (RRR), and whether such discrimination is influenced by presentation of baseline risk. Methods: The study was a randomised cross-sectional interview survey of a representative sample (n = 1,519) of lay people with mean age 59 (range 40-98) years in Denmark. In addition to demographic information, respondents were asked to consider a hypothetical drug treatment to prevent heart attack. Its effectiveness was randomly presented as RRR of 10, 20, 30, 40, 50 or 60 percent, and half of the respondents were presented with quantitative information on the baseline risk of heart attack. The respondents had also been asked whether they were diagnosed with hypercholesterolemia or had experienced a heart attack. Results: In total, 873 (58%) of the respondents consented to the hypothetical treatment. While 49% accepted the treatment when RRR = 10%, the acceptance rate was 58-60% for RRR>10. There was no significant difference in acceptance rates across respondents irrespective of whether they had been presented with quantitative information on baseline risk or not. Conclusion: In this study, lay people's decisions about therapy were only slightly influenced by the magnitude of the effect when it was presented in terms of RRR. The results may indicate that lay people have difficulties in discriminating between levels of effectiveness when they are presented in terms of RRR.
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Background
Patient autonomy is a core element of medical ethics.
Patient autonomy implies that patients and doctors share
responsibility for medical decision to the extent patients
wish to be included. For shared decision making to be
meaningful, however, patients need to have an
understanding of the effectiveness of medical interventions.
This usually requires the use of the risk concept.
Communicating risk information is therefore a fundamental and
increasingly prominent part of medical practice. Effective
risk communication can enhance knowledge,
involvement in decisions about testing or treatment, autonomy
and empowerment of patients [1]. However poor
communication may possibly lead to anxiety or lack of
confidence in health care professionals [2]. It is vital that we
identify the available evidence about how risk
communication should best be done.
The effectiveness of an intervention for a chronic disease
may be presented in terms of Relative Risk Reduction
(RRR), Absolute Risk Reduction (ARR), Numbers Needed
to Treat (NNT), or Odds Ratio (OR). These measures may
subsequently be translated into increased (disease-free)
life expectancy because the intervention postpones
adverse events. The choice of effect measure has been
discussed extensively in the scientific literature (e.g. by
Gigerenzer et al [3] or Elmore et al [4]), but we still need more
knowledge about how intervention effectiveness can be
communicated to patients, doctors and health
administrators.
Decisions should, in line with expected utility theory [5],
be based on the absolute risk reductions (or its reciprocal
NNT) even though this principle in practice is frequently
violated. However, there is evidence that lay-persons and
professionals may have difficulties in understanding NNT
[6-8]. Great effectiveness of a treatment corresponds with
low value of NNT, and this may mislead patients if they
associate great effectiveness with a large number. In
contrast, for RRR a greater value means greater effectiveness.
RRR, however, may be misleading because it usually is
greater than ARR numerically, and may consequently
"exaggerate" the treatment effect. Still, RRR is frequently
presented in the medical literature, possibly because it is
more stable across patient groups than ARR [9]. It is
therefore conceivable that doctors on some occasions use RRR
in their communication with patients. Even though
decisions should not be based on RRR alone, we need to know
to which extent patients can utilise information about
RRR. We have searched the literature without finding any
direct evidence of the extent to which lay people
understand RRR.
The size of baseline risk has been shown to influence
acceptance of a hypothetical treatment [ (...truncated)