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Ann Epidemiol. 2009 May;19(5):316-22. doi: 10.1016/j.annepidem.2009.01.001. Epub 2009 Feb 20.

The effect of a physical activity intervention on bias in self-reported activity.

Author information

1
Department of Epidemiology, University of North Carolina, Chapel Hill, NC 27599, USA. dtaber@email.unc.edu

Abstract

PURPOSE:

A positive outcome in self-reported behavior could be detected erroneously if an intervention caused over-reporting of the targeted behavior. Data collected from a multi-site randomized trial were examined to determine if adolescent girls who received a physical activity intervention over-reported their activity more than girls who received no intervention.

METHODS:

Activity was measured using accelerometers and self-reports (3-Day Physical Activity Recall, 3DPAR) in cross-sectional samples preintervention (6th grade, n = 1,464) and post-intervention (8th grade, n = 3,114). Log-transformed accelerometer minutes were regressed on 3DPAR blocks, treatment group, and their interaction, while adjusting for race, body mass index, and timing of data collection.

RESULTS:

Preintervention, the association between measures did not differ between groups, but post-intervention 3DPAR blocks were associated with fewer log-accelerometer minutes of moderate-vigorous physical activity (MVPA) in intervention girls than in control girls (p = 0.002). The group difference was primarily in the upper 15% of the 3DPAR distribution, where control girls had >1.7 more accelerometer minutes of MVPA than intervention girls who reported identical activity levels. Group differences in this subsample were 8.5%-16.2% of the mean activity levels; the intervention was powered to detect a difference of 10%.

CONCLUSION:

Self-report measures should be interpreted with caution when used to evaluate a physical activity intervention.

PMID:
19230711
PMCID:
PMC2746093
DOI:
10.1016/j.annepidem.2009.01.001
[Indexed for MEDLINE]
Free PMC Article
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