Idea: In advising on the most effective measures to be taken to improve the health of a population, epidemiologists may focus on different determinants of the disease than a doctor would when faced with sick or high-risk individuals.

Rose (1985) promotes the population health focus, but this is not universally accepted by healthcare practitioners and policy makers.  If someone asks you the question Rose’s mentor posed, “Why did this patient get this disease at this time?,” how do you answer?  Can you identify areas in your own life and/or work when you would take a population view and other areas where your focus would be individually-centered?

(Repeating text from a recent post):  Road accidents and alcohol consumption may be a good illustration of Rose’s argument. Most of us know of getting home safely when we’ve drunk too much “risk factor,” but we also know that a substantial fraction of people in accidents have high alcohol levels. We also sense that some people are more susceptible to having their judgement and reaction times impaired by alcohol so we could imagine doing further epidemiological and biological research to develop multivariable risk factor formulas. Would a more refined knowledge of riskiness help us prioritize our risk-prevention efforts, or would that pale into insignificance relative to a Rosean drink-don’t-drive efforts?

Controversy over vaccination of girls for HPV, given the physical side effects (at a low rate — see http://www.usatoday.com/news/health/2009-08-31-hpv-gardasil_N.htm) and promiscuity-inducing side effects (no data for this). Question: What would Rose propose?

Question: Why isn’t a population an aggregation of individuals and thus population risk = sum of individual risks?
My response: 1. It is necessary to think of different meaning of “treatment.” A sick individual is treated by a physician to cure or reduce the effects of the disease. Population health policies do not treat a large group of sick people, but attempt to reduce the incidence in the next generation.

2. A physician treating sick individuals adjusts the treatment for individuals if it doesn’t work well for them.  In contrast, public health measures usually discount the heterogeneity in the population and apply the same policy to all.   Nevertherless, it is possible to imagine that knowledge of heterogeneous responses to treatment of individuals could lead to more effective population health policies (and reduce the kickback that occurs when some individuals claim to have suffered under the population health policy).

(This post continues a series laying out a sequence of basic ideas in thinking like epidemiologists, especially epidemiologists who pay attention to possible social influences on the development and unequal distribution of diseases and behaviors in populations [see first post in series].)

Reference

Rose, G. (1985). “Sick individuals and sick populations.” International Journal of Epidemiology 14: 32-38. Reprinted in IJE 30: 427-432 (2001)