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Editor's Correspondence
July 12, 2010

Analysis of Television Viewing and Physical Activity Using Time Substitution Models

Author Affiliations

Author Affiliations: Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts.

Arch Intern Med. 2010;170(13):1173-1174. doi:10.1001/archinternmed.2010.210

Television (TV) watching time poses unique challenges in analysis. Recently, Otten at al1 described the effects of reducing TV viewing time on energy intake and expenditure in overweight and obese adults in a randomized controlled trial. Although a reduction in TV viewing produced a significant increase in total daily energy expenditure among those randomized to TV restriction compared with the control group, the authors also found a nonsignificant decrease in energy intake in both groups. However, the analysis of TV viewing time was carried out using multivariate models that did not account for effects of varying time displacement and relative time substitution, nor did it control for the confounding effect of total activity time. An analysis of reducing TV watching time without considering these issues may lead to bias and incomplete interpretation of the effects of decreasing TV watching time.2

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