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Manuel and colleagues actually advocate for better assessment of population risk, not a high-risk approach

Posted by dgmanuel on 23 Sep 2010 at 14:40 GMT

Capewell and Graham quoted our study to say that we “advocated the high risk approach” when we actually wrote: “We have purposely avoided stating which strategy, population or (high) baseline risk, is potentially more effective for reducing coronary heart disease”.(1;2) Tellingly, true advocates for a high-risk approach have been equally critical (if not more so) saying that our study underestimated the effectiveness of a high-risk approach(3) – often assuming that we support a community-wide approach. Capewell and Graham so misrepresented our study that it raises the concern they may have erroneously quoted other studies or that there is an unbalanced presentation of the literature.

We argued that population risk is a cornerstone of population health planning, as articulated by Rose, and that modern approaches of estimating population risk should be developed and used.(4) Too often, advocates of community-wide strategies assume that population risk is diffused without actually describing the risk. Equally common, advocates of a high-risk approach demonstrate that treatment is effective in a small group of high-risk people and then recommend therapy to a large proportion of the total population – many or most of whom are a low-risk, so do not contribute to population burden. In our study we advocated for better assessment of the potential population effectiveness and efficiency of different prevention strategies.

Contrary to Capewell’ and Graham’s assertion, we did not ignore the issue of under-treatment or adherence or assume that community-wide strategies could only achieve a 2% reduction in population cholesterol. Rather, we examined the level of adherence required for a high risk strategy to achieve the same effectiveness as each 2% reduction in cholesterol. Our study estimated 16% adherence to a high-risk strategy was required to achieve the equivalent effectiveness of a 2% reduction in population cholesterol in Canada, 1990. There are populations where cholesterol has decreased more than 2%, but also many examples where community-wide strategies have not been as effective or even where cholesterol levels have increased. Similarly, there is a wide range of population coverage of statins.

There are plenty of examples where both community-wide and high-risk strategies have been ineffective and/or resulted in increased inequity. Fortunately, in most countries, there has been a substantial decrease in cardiovascular disease–usually accompanied by narrowing mortality by income groups. In Canada, the narrowing is considerable and likely a result of both community-wide and high-risk interventions. However, inequities for lung cancer have persisted or increased – raising concern that the strategy for smoking prevention in Canada (community-wide approach) has not been equitable to date.(5)

Capewell and Graham rightly conclude that there is usually a role for both high-risk and community-wide strategies. The population effectiveness of different strategies depends on several critical factors that were described by Capewell and Graham–including the diffusion or concentration of risk and achievement of high and equitable strategy coverage.(4) Typically, population risk is neither completely diffused nor concentrated. Similarly, health inequities have the potential to narrow or widen under both strategies – depending on whether each strategy is well or poorly implemented. The challenge for any disease or population setting is finding the right balance between different preventive strategies, if there are limited resources, and to maximize the role of all strategies for reducing inequities.

Douglas G. Manuel, Senior Scientist, Ottawa Hospital Research Institute

(1) Capewell S, Graham H. Will cardiovascular disease prevention widen health inequalities? PLoS Med 2010;7:e1000320.
(2) Manuel DG, Lim J, Tanuseputro P, Anderson GM, Alter DA, Laupacis A, Mustard CA. Revisiting Rose: strategies for reducing coronary heart disease. Br Med J 2006;332:659-62.
(3) Genest J, McPherson R, Frohlich J, Fodor G. The analysis by Manuel and colleagues creates controversy with headlines, not data. CMAJ 2005;172:1033-4.
(4) Manuel DG, Rosella LC. Commentary: Assessing population (baseline) risk is a cornerstone of population health planning--looking forward to address new challenges. Int J Epidemiol 2010;39:380-2.
(5) James PD, Wilkins R, Detsky AS, Tugwell P, Manuel DG. Avoidable mortality by neighbourhood income in Canada: 25 years after the establishment of universal health insurance. J Epidemiol Community Health 2007;61:287-96.

No competing interests declared.