Effect of age of entry to a longitudinal study on cross-sectional determination of cardiovascular disease

Abstract

Cross-sectional analysis from longitudinal studies for a specific age can include subjects who entered the study at different ages (i.e. younger individuals followed to the age of interest, and those who entered at the age of interest). This represents a potential source of bias, since the state of health at a given age may vary based on age at entry. We investigated such bias as it affected the prevalence of cardiovascular diagnoses in men from the Baltimore Longitudinal Study of Aging. Subjects who entered the study in either their 60′s, 70′s or 80′s (New subjects) were compared to individuals who entered the study at an age at least 10 years younger and were followed into these same age decades (Continuing subjects). No differences were found between New and Continuing subjects for coronary heart or cerebrovascular diseases, but were present for hypertension. The greater prevalence of hypertension in Continuing subjects appeared to be of minor clinical importance because other diagnostic differences were absent. The study found evidence for potential selection bias based on age at entry, but the consequence of the bias appeared to be slight. (Aging 3: 355-360, 1991)