Question

1. The number of sudden cardiac death occurring in the United States ranges between 180,000 to 450,000 cases annually. To identify salient predictors of sudden cardiac arrest, an investigator recruited a sample of 2,000 men and women who were aged 40 years or older and were surveyed during 1988-1994 with no history cardiovascular disease and living in metropolitan areas. The response rate for this study was 100%. Information on several risk factors with the exception of smoking were obtained. During the 30 year long study which ended on decomenter 31, 2018, 180 cases of sudden cardiac death occurred with the events being higher among those who had a pre-existing coronary event. The population attributable risk of smoking on sudden cardiac death was reported to be 39% while the population attributable risk for obesity was reported to be 55% by the investigator.

Very briefly, explain why the population attributable risk is (or is not) the appropriate measure of association to be reported for this study?

Answer 1

Cardiovascular disease (CVD) is a leading cause of death in United States. To reduce the threat of CVD, it is important to identify its major risk factors. The population attributable fraction (PAF) is calculated from the prevalence and relative risk of risk factors and can be used to estimate the burden of these factors with respect to CVD. We analyzed the findings from several prospective studies to determine the PAFs of CVD.

Cardiovascular diseases (CVDs), namely, heart disease and stroke, are leading causes of death in United States. Furthermore, because stroke is a major cause of certification for long-term care insurance in United States, risk factors for stroke also contribute to a decline in activities of daily living (ADL). Therefore, the prominent risk factors for CVD must be identified if we are to lower the risks for mortality and ADL decline. The population attributable fraction (PAF) is an estimate of the burden of a disease. My colleagues and I estimated the PAFs of all-cause death, CVD death, CVD incidence, ADL decline, and smoking-related diseases due to established CVD risk factors, and the results are described herein.

The CARDIA study, a biethnic, prospective, multicenter epidemiologic study of the evolution of risk factors in young adults, has been described in detail elsewhere. Briefly, from 1985 to 1986, 5115 African-American and white adults aged 18 to 30 years were examined in Birmingham, AL, Chicago, IL, Minneapolis, MN, and Oakland, CA. At the Birmingham, Minneapolis, and Chicago sites, participants were randomly selected from total communities or from specific census tracts. In Oakland, participants were randomly selected from members of the Kaiser Permanente Medical Care Program. At each site, recruitment achieved nearly equal numbers with respect to race (African American, white), sex, education (high school or less, more than high school), and age (18–24 years, 25–30 years). Fifty percent of invited individuals contacted were examined (47% of African Americans and 60% of whites) and formed the CARDIA cohort.

The ARIC Study is a multicenter prospective cohort study investigating the natural history of atherosclerotic disease in the US communities of Forsyth County, NC, Jackson, MI, Washington County, MD, and the northwest suburbs of Minneapolis, MN. At baseline, in 1987–89, the cohort comprised 15 792 men and women aged 45 to 64 years who were selected by using a list or area probability sampling. Race/ethnicity was self-reported; only African Americans were recruited in the Jackson study center. The baseline home interview assessed participant sociodemographic characteristics, smoking and alcohol-drinking habits, medication use, and personal history of diseases.

Calculation of population attributable fraction

PAF was calculated using the formula: PAF = pd × (relative risk − 1)/relative risk, where pd is the proportion of cases exposed to the risk factor.