From their days in training through their years of practice, family physicians emphasize preventive medicine. They counsel patients on diet and exercise, safe sex, and substance abuse; screen for early detection of cancer (eg, cervical, breast, colon, prostate); and administer chemo- and immunoprophylaxis (daily aspirin, vaccinations).
Though physicians are accustomed to caring for individuals, adopting a population perspective—considering the practice’s patient panel or even the larger community—is a logical extension of one’s daily practice. The public’s health benefits from parallel efforts in risk assessment and community-wide prevention. And, as we propose here, awareness of the similarities between the 2 areas of endeavor strengthens both.
Assessing risk for the individual
Risk factors are characteristics of a person that increase the likelihood of becoming diseased. Obvious risk factors include physical traits and laboratory values such as obesity, high cholesterol levels, and high blood pressure, and behaviors such as smoking and binge drinking. Other risk factors include demographic traits (age, race/ethnicity, gender, income), environmental influences (occupation, geographic location), and system issues (insurance status, usual source of care). Though risk factors may not cause disease, their presence can increase the probability that disease will eventually develop.
The degree to which a risk factor may influence disease development can be calculated with 2 measures.
Absolute risk is the difference between the incidence of disease in the group exposed to a risk factor and the incidence in the group not exposed to the factor.
Relative risk is the extent to which persons exposed to a risk are likely to develop the disease compared with those not exposed (see Calculating relative risk). Relative risk is more useful for judging a factor’s strength of disease causality, but it does not necessarily indicate the magnitude of risk for a population. With an uncommon disease, for instance, the relative risk of disease from an exposure may be large but the absolute risk may be small.
Calculating relative risk
Relative risk = (a/a+b) / (c/c+d)
Relative risk—the likelihood that those exposed to a risk factor for disease will become diseased, compared with those not exposed to the factor—is calculated as follows:
Relative risk = (a/a+b) / (c/c+d)
The incidence of disease among those exposed (a divided by a+b) divided by the indicence of disease among those not exposed (c divided by c+d).
For more on relative risk, see “Relative risks and odds ratios: What’s the difference?,” in the February 2004 JFP.
Assessing risk for a population
Just as absolute and relative risk help quantify an individual’s susceptibility to disease, the population attributable risk helps gauge the level of risk to a community. The calculation takes into account disease incidence as well as how often the population is exposed to a related risk factor. This measure can be particularly influential in health policy decisions such as how to spend scarce resources—illustrated in the following example.2
Individual and population risks are determined in part by the prevalence of a risk factor. Consider the risk of death in the case of hypertension. For an individual, the risk of death is greater with severe hypertension than with mild hypertension. However, mild hypertension is quite common; severe hypertension is not. Therefore, the population attributable risk of hypertension (the number of extra deaths in the population attributable to hypertension) is greater for those with mild hypertension, even though the risk to an individual is greatest when hypertension is severe. This suggests that more lives can be saved by treating lots of people who have mild hypertension than by treating the much smaller number of people with severe hypertension—a concept called the “prevention paradox,” and one that underlies a number of national prevention efforts.
Synergies between individual and community prevention
Individual and community prevention strategies both have merit. For example, public health smoking cessation campaigns have been effective at the population level. At the same time, physician efforts to promote smoking cessation through office counseling sessions are effective with individuals. Individual physician efforts become population efforts if thousands of physicians each day provide cessation counseling to their patients. Public health campaigns help accomplish this by reinforcing the importance of cessation efforts including those delivered by practicing physicians.
Another excellent example of this type of reinforcing synergy is the work of the past decade to address hyperlipidemia as a risk factor for heart disease. In this effort, physician screening and treatment of patients has been both promoted and complemented by national media campaigns, local health fairs, and ongoing research, to the point where many individuals now are familiar with cholesterol and want to know their own lipid values.