Sources of variance in daily physical activity levels in the seasonal variation of blood cholesterol study

UMMS Affiliation

Department of Medicine, Division of Preventive and Behavioral Medicine; Department of Medicine, Division of Cardiovascular Medicine

Publication Date


Document Type



*Activities of Daily Living; Adult; Aged; Cholesterol; Epidemiologic Studies; Female; Humans; Longitudinal Studies; Male; Middle Aged; Occupations; *Physical Fitness; Recreation; Reproducibility of Results; *Seasons


Biochemical Phenomena, Metabolism, and Nutrition | Cardiology | Cardiovascular Diseases | Environmental Public Health | Epidemiology | Lipids | Musculoskeletal, Neural, and Ocular Physiology | Polycyclic Compounds


The authors examined sources of variance in self-reported physical activity in a cohort of healthy adults (n = 580) from Worcester, Massachusetts (the Seasonal Variation of Blood Cholesterol Study, 1994-1998). Fifteen 24-hour physical activity recalls of total, occupational, and nonoccupational activity (metabolic equivalent-hours/day) were obtained over 12 months. Random effects models were employed to estimate variance components for subject, season, day of the week, and residual error, from which the number of days of assessment required to achieve 80% reliability was estimated. The largest proportional source of variance in total and nonoccupational activity was within-subject variance (50-60% of the total). Differences between subjects accounted for 20-30% of the overall variance in total activity, and seasonal and day-of-the-week effects accounted for 6% and 15%, respectively. For total activity, 7-10 days of assessment in men and 14-21 days of assessment in women were required to achieve 80% reliability. For nonoccupational activity, 21-28 days of assessment were required. This study is among the first to have examined the sources of variance in daily physical activity levels in a large population of adults using 24-hour physical activity recall. These findings provide insight for understanding the strengths and limitations of short term and long term physical activity assessments employed in epidemiologic studies.


epidemiologic measurements, exercise, reproducibility of results, seasons, MET(s), metabolic equivalent(s), SD, standard deviation, SEASON, Seasonal Variation of Blood Cholesterol

DOI of Published Version



Am J Epidemiol. 2001 May 15;153(10):987-95.

Journal/Book/Conference Title

American journal of epidemiology

Related Resources

Link to article in PubMed

PubMed ID