a case for incremental risk communication in SNP-based, common-chronic disease risk
oi, life has been busy indeed. as i delay my packing for the American College of Medical Genetics meeting in Albuquerque yet another hour past midnight, here is something i have been working on that has been particularly interesting to me: risk communication in public health. as of my public health courses, i of course bring in my knowledge and interests around genetic testing and emerging genetic technologies into play. here is a sample of a short piece i wrote discussing the idea of emphasizing incremental risk…
Incremental Risk Communication and Common Genetic Variant Risks
The framing of numerical risk comparisons as incremental values when compared to showing risk figures as simply a comparison of absolutes risks has been show to better focus the target audience’s attention on specifically the change from baseline risk (Zikmund-Fisher B, Fagerlin A, Roberts A, Derry H, et al 2008). In the context of genetic risk communication and genetic counseling for many highly-penetrant and/or mendelian-inherited disorders, the risk of developing symptoms and risk of inheritance, respectively, garner considerably less utility in highlighting incremental risks given the often extreme differences that exist in these risks when compared to the general population. In stark contrast are those risks conferred to individuals when common genetic variants, such as those ascertained through many recent genome-wide association studies imparting minimal to modest risks, many with a relative risk under 2 (Eng C and Sharp R, 2010). Among a slew of complex ethical, legal, and social issues surrounding the reliability and clinical utility of communicating these common variant risk modifications to the public, an underlying methodological issue has been how a genetic counselor can actually communicate such small relative risk figures without misrepresenting the actual changes in baseline risks and increase in risk due to a variant. A potential solution lies in the communication of incremental risks in the methods that the authors of Zikmund-Fisher et al. 2008 demonstrate, focusing on comparison of baseline, absolute risks and the incremental changes attributed to presence of a common genetic variant.
In order to properly frame the utility of incremental risk in this scenario, a hypothetical discussion of an individual with a baseline heart disease risk of 14%, and a testable, validated common genetic variant will exist, with an relative risk of 1.3 affecting heart disease in individuals of this population, will be presented. One technique normally found in the genetic counselor’s repertoire in risk communication has been to state baseline risks, and then to provide the odds ratio of possessing the common variant in multiple formats. These multiple relative risk formats could be framed as “1.3 times greater chance of heart disease”, shown that the variant provides “30% more risk”, or provided as the absolute risk of an individual with the common variant to be 18.2% for heart disease. None of these techniques, however, highlight the “marginal increment in risk while simultaneously providing information about baseline risk level for context” (Zikmund-Fisher et al. 2008). Instead, framing the change in risk of an individual that possesses our proposed common variant through incremental risk, may highlight the change in risk more accurately without the need for more high numeracy-requiring processes of mental math: multiplying relative risks against baseline or subtracting absolute final risks from baseline.
In this scenario of highlighting incremental risk, the communicated risks would thus be provided as a baseline, absolute risk for heart disease of 14%, while individuals possessing the common variant experience an incremental absolute increase of 4.2% risk for heart disease, providing a total of 18.2% absolute risk. While the authors of Zikmund-Fisher et al. 2008 acknowledge that providing incremental risk altered the degree of worry in participants, without knowing what the appropriate degree of worry should be among these individuals, the focus on the specific change in absolute risk more accurately distinguishes for audiences the most important element of the risk communication.
Zikmund-Fisher BJ, Fagerlin A, Roberts TR, Derry HA, Ubel PA. Alternate methods of framing information about medication side effects: Incremental risk versus total risk of occurrence. Journal of Health Communication 2008;13(2):107-24.