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Background: Physical activity and sedentary behavior are associated with health outcomes. However, evidence may be affected by confounding bias. This study aimed to examine the relationships of physical activity and television (TV) viewing time with all-cause, cardiovascular, and cancer mortality in a cohort of Australian adults, and determine the robustness of these relationships to residual and unmeasured confounding., Methods: Data from 27,317 Melbourne Collaborative Cohort Study participants (mean age = 66) were used. Physical activity was assessed using the International Physical Activity Questionnaire-Short Form and categorized as insufficient, sufficient, or more than sufficient. TV viewing time was categorized as low, moderate, or high. Multivariable Cox regression models were used to evaluate associations of interest. E-values were calculated to assess the strength of unmeasured confounders required to negate the observed results., Results: For highest versus lowest physical activity category, the hazard ratio was 0.67 (95% confidence interval, 0.56-0.81) for all-cause mortality; E-values ranged between 1.79 and 2.44. Results were similar for cardiovascular mortality; however, hazard ratios were lower (0.72; 95% confidence interval, 0.51-1.01) and E-values much smaller (1.00-2.12) for cancer mortality. For highest versus lowest TV viewing time category, the hazard ratio was 1.08 (1.01-1.15) for all-cause mortality; E-values ranged between 1.00 and 1.37. Results were similar for cardiovascular and cancer mortality., Conclusions: Physical activity and TV viewing time were associated with mortality. The robustness to unmeasured/residual confounding was moderate for physical activity (all-cause and cardiovascular mortality), but weaker for physical activity (cancer mortality) and TV viewing time in this study of Australian adults.

Objectives: To estimate the extent of measurement error in the Active Australia questionnaire, and to examine the impact of measurement error on the association of moderate-vigorous physical activity (MVPA) with obesity., Design: Accelerometer Validation Study, cross-sectional; data from the third wave of a prospective cohort (Australian Diabetes, Obesity, and Lifestyle (AusDiab) Study))., Methods: Self-reported physical activity data were obtained from 4005 participants of the third wave of the AusDiab study via the Active Australia questionnaire. Accelerometer-derived physical activity data were obtained from a subsample of 670 participants. Validity coefficients and attenuation factors were estimated from a measurement error model. A regression calibration method was applied to a logistic regression model examining the association between self-reported MVPA and obesity to adjust observed odds ratios (OR) for measurement error., Results: The validity coefficient was 0.35 (0.28, 0.43) and the attenuation factor was 0.16 (0.13, 0.20) in models adjusted for age and sex. The uncorrected OR for obesity for 210min/week of MVPA (50th percentile) relative to 80min/week (25th percentile) was 0.87 (0.85, 0.90). The attenuation factor was used to adjust this OR for measurement error, giving a corrected OR of 0.43 (0.32, 0.55)., Conclusions: Substantial measurement error (relative to accelerometry) was evident in the Active Australia questionnaire, leading to attenuation of the association of MVPA with obesity. A regression-calibration method can be used to adjust risk estimates for associations between self-reported MVPA and health-related outcomes for measurement error specific to self-report. These corrected risk estimates reflect associations that would be expected if MVPA were measured by accelerometry., (Copyright © 2020 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.)