Seigo Urushidani, MD; Akira Kuriyama, MD, MPH
Disclosures: Authors have disclosed no conflicts of interest. Forms can be viewed at www.acponline.org/authors/icmje/ConflictOf InterestForms.do?msNum=L15-0180.
Urushidani S., Kuriyama A.; Sedentary Time and Risk for Mortality. Ann Intern Med. 2015;162:875. doi: 10.7326/L15-0180
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Published: Ann Intern Med. 2015;162(12):875.
TO THE EDITOR:
Biswas and colleagues (1) did a meta-analysis of observational studies to examine the association between sedentary time and various health outcomes. Their analysis suggested that sedentary time was associated with an increased risk for all-cause mortality but was substantially heterogeneous (I2 = 94.96%). We wonder whether further sensitivity analyses are needed to elucidate the cause of this heterogeneity.
First, sample sizes varied across studies, ranging from 217 to 240 819. A forest plot suggested that 5 of the 7 studies with fewer than 10 000 participants presented more exaggerated point estimates of hazard ratios than the remaining 8 studies. In clinical trials in medicine, large treatment effects are known to be derived from small trials (2). Likewise, smaller observational studies could be hypothesized to present larger hazard ratios than larger studies. An analysis examining the association between sample size and all-cause mortality might therefore be intriguing.
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