Mekary and Ding cite their recent research article1 on isotemporal substitution paradigm as a possible model for analyzing the result of our study.2 We acknowledge that this is an interesting new model for analyzing the relative effects of replacing one activity, such as TV viewing, with another, such as brisk walking. The model appears to be most appropriate in large-scale, prospective epidemiological studies.
Otten JJ, Littenberg B, Harvey-Berino J. Analysis of Television Viewing and Physical Activity Using Time Substitution Models—Reply. Arch Intern Med. 2010;170(13):1173-1174. doi:10.1001/archinternmed.2010.211