Academic journal article Generations

Reading Public Health Research: Understanding Risk Factors and the Epidemiological Approach

Academic journal article Generations

Reading Public Health Research: Understanding Risk Factors and the Epidemiological Approach

Article excerpt

Clear explanations for practitioners in aging.

The second fifty years of life are marked by an increasing prevalence of chronic disease (along with an increased risk of mortality from such disease), as well as an increase in disease burden, which is evident in persistent disability, increased use of medical and supportive care services, and the ever more difficult challenge of maintaining high function following hospitalization and rehabilitation.

As used here, the words risk and disease burden are technical terms drawn from epidemiology, "the study of the distribution and determinants of disease frequency" (MacMahon and Pugh, 1970). A basic understanding of epidemiology is critical for understanding the public health challenge of an aging world. Epidemiology provides tools for establishing the frequency of disease and potential differences in this frequency between populations or subgroups within a population. With these characteristics established, one can determine sources of variation in the risk of disease. Recognizing differences in the frequency and distribution of disease points to risk factors and hence the causal pathway, or etiology, of a disease. Once we have identified these pathways, we can break the causal chain. Epidemiology is a key element in the public health goal of developing interventions and preventive strategies likely to reduce the risk of disease and the burden associated with it.

In this brief review, we will examine key epidemiological terms used in aging and public health research, basic research designs for promoting public health among older adults, and selected studies that show the promise of a public health approach to aging.


In public health, the term prevalence refers to the number of people with a condition at a given time. Prevalence is expressed as a proportion, for example, the number of cases per 10,000 people ages 65-plus. Prevalence combines newly diagnosed and already existing cases. Thus, the prevalence of a given condition will depend both on the rate of new cases and on how long people live with the condition. Survival with a health condition, in turn, depends on available treatments, the rate at which the disease progresses, whether treatments are appropriately applied, other health conditions a person may face, environmental and social supports, and much more. Because of these features, prevalence estimates are most useful for assessing the most general impact of a health condition and for estimating the medical and supportive care needs of people likely to be affected by it.

Prevalence is commonly reported by public health agencies. For example, a recent compendium from the Centers for Disease Control and Prevention (CDC) (2003) reports that about 80 percent of people ages 65-plus have tine or more chronic conditions, and 50 percent have two or more. Nearly 20 percent have diabetes. Some 60 percent have arthritis. Some 6 percent to 10 percent have Alzheimer's disease, with AD prevalence increasing to nearly 50 percent in people ages 85-plus.

The term incidence, by contrast, refers to new cases in a population over a defined time interval. It is a rate -for example, the number of newly diagnosed cases per 10,000 people followed for one year, or per 10,000 person-years. Incidence is most useful for establishing ctiological factors. Because it is limited to new cases, differences in incidence between populations indicate differences in risk, and hence point to factors (i.e., differences between the populations) that lower or elevate risk. "Hie excess risk associated with an criological factor is usually expressed as a risk ratio (RR), which is simply incidence in the group with the eriologic factor divided by incidence in the yroup without.

Incidence studies have been very valuable for identifying risk factors, especially in the case of falling and disability. In the Yale FICSIT trial (Frailty and Injuries Cooperative Studies of Intervention Techniques), 35 percent of the intervention group fell over a one-year period, compared to 47 percent of those in the control group (which did not receive the intervention) (Tinetti et al. …

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