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Adjustment for physical activity in studies of sedentary behaviour.

Page A, Peeters G, Merom D - Emerg Themes Epidemiol (2015)

Bottom Line: Sedentary behaviour (too much sitting, as distinct from too little exercise) has emerged as a potentially significant public health issue.Analytically, researchers have reported 'independent' associations between sedentary behaviour (SB) and a number of health outcomes by adjusting for physical activity (PA) (and other confounders), and conclude that SB is associated with the outcome even in those who are physically active.However, the logical rationale for why adjustments for PA are required is often not delineated, and as a consequence, PA has been conceptualised as a confounder, an intermediary, and an effect measure modifier-sometimes simultaneously-in studies of SB and health outcomes.

View Article: PubMed Central - PubMed

Affiliation: Centre for Health Research, School of Medicine, University of Western Sydney, Campbelltown, Australia.

ABSTRACT
Sedentary behaviour (too much sitting, as distinct from too little exercise) has emerged as a potentially significant public health issue. Analytically, researchers have reported 'independent' associations between sedentary behaviour (SB) and a number of health outcomes by adjusting for physical activity (PA) (and other confounders), and conclude that SB is associated with the outcome even in those who are physically active. However, the logical rationale for why adjustments for PA are required is often not delineated, and as a consequence, PA has been conceptualised as a confounder, an intermediary, and an effect measure modifier-sometimes simultaneously-in studies of SB and health outcomes. This paper discusses the analytical assumptions underlying adjustment for PA in studies of SB and a given outcome, and considers the implications for associations between SB and health.

No MeSH data available.


Physical activity as a common cause (confounder) of sedentary behaviour and disease outcomes. a PA is a common cause of SB and the outcome (D). C is an exogenous variable that is a common cause of both PA and SB. b The causal direction between PA and SB is unknown. C is an exogenous variable that is a common cause of both PA and SB. c PA is a common cause of SB and the outcome (D), with sub-scripts denoting measurement at time 1 and time 2. C is an exogenous variable that is a common cause of both PA and SB.
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Fig1: Physical activity as a common cause (confounder) of sedentary behaviour and disease outcomes. a PA is a common cause of SB and the outcome (D). C is an exogenous variable that is a common cause of both PA and SB. b The causal direction between PA and SB is unknown. C is an exogenous variable that is a common cause of both PA and SB. c PA is a common cause of SB and the outcome (D), with sub-scripts denoting measurement at time 1 and time 2. C is an exogenous variable that is a common cause of both PA and SB.

Mentions: Analytically, researchers obtain ‘independent’ associations between sedentary behaviour (SB) and a given outcome by adjusting for physical activity (PA), and conclude that SB is associated with the outcome even in those who are physically active (that is, achieving recommended MVPA). By including PA and SB simultaneously in a statistical model, there is an implied causal assumption, illustrated by the directed acyclic graphs in Figures 1 and 2. If PA is considered a common cause (confounder) of SB and the outcome (D), the implication is that PA causes SB (Figure 1a), and adjustment is necessary. There may also be an exogenous variable (C), such as injury or disability status, which is a common cause of both PA and SB, and where the causal direction between PA and SB is unknown. In this case adjustment for PA is necessary if C is unmeasured and PA is not collinear with SB (Figure 1b).Figure 1


Adjustment for physical activity in studies of sedentary behaviour.

Page A, Peeters G, Merom D - Emerg Themes Epidemiol (2015)

Physical activity as a common cause (confounder) of sedentary behaviour and disease outcomes. a PA is a common cause of SB and the outcome (D). C is an exogenous variable that is a common cause of both PA and SB. b The causal direction between PA and SB is unknown. C is an exogenous variable that is a common cause of both PA and SB. c PA is a common cause of SB and the outcome (D), with sub-scripts denoting measurement at time 1 and time 2. C is an exogenous variable that is a common cause of both PA and SB.
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4496859&req=5

Fig1: Physical activity as a common cause (confounder) of sedentary behaviour and disease outcomes. a PA is a common cause of SB and the outcome (D). C is an exogenous variable that is a common cause of both PA and SB. b The causal direction between PA and SB is unknown. C is an exogenous variable that is a common cause of both PA and SB. c PA is a common cause of SB and the outcome (D), with sub-scripts denoting measurement at time 1 and time 2. C is an exogenous variable that is a common cause of both PA and SB.
Mentions: Analytically, researchers obtain ‘independent’ associations between sedentary behaviour (SB) and a given outcome by adjusting for physical activity (PA), and conclude that SB is associated with the outcome even in those who are physically active (that is, achieving recommended MVPA). By including PA and SB simultaneously in a statistical model, there is an implied causal assumption, illustrated by the directed acyclic graphs in Figures 1 and 2. If PA is considered a common cause (confounder) of SB and the outcome (D), the implication is that PA causes SB (Figure 1a), and adjustment is necessary. There may also be an exogenous variable (C), such as injury or disability status, which is a common cause of both PA and SB, and where the causal direction between PA and SB is unknown. In this case adjustment for PA is necessary if C is unmeasured and PA is not collinear with SB (Figure 1b).Figure 1

Bottom Line: Sedentary behaviour (too much sitting, as distinct from too little exercise) has emerged as a potentially significant public health issue.Analytically, researchers have reported 'independent' associations between sedentary behaviour (SB) and a number of health outcomes by adjusting for physical activity (PA) (and other confounders), and conclude that SB is associated with the outcome even in those who are physically active.However, the logical rationale for why adjustments for PA are required is often not delineated, and as a consequence, PA has been conceptualised as a confounder, an intermediary, and an effect measure modifier-sometimes simultaneously-in studies of SB and health outcomes.

View Article: PubMed Central - PubMed

Affiliation: Centre for Health Research, School of Medicine, University of Western Sydney, Campbelltown, Australia.

ABSTRACT
Sedentary behaviour (too much sitting, as distinct from too little exercise) has emerged as a potentially significant public health issue. Analytically, researchers have reported 'independent' associations between sedentary behaviour (SB) and a number of health outcomes by adjusting for physical activity (PA) (and other confounders), and conclude that SB is associated with the outcome even in those who are physically active. However, the logical rationale for why adjustments for PA are required is often not delineated, and as a consequence, PA has been conceptualised as a confounder, an intermediary, and an effect measure modifier-sometimes simultaneously-in studies of SB and health outcomes. This paper discusses the analytical assumptions underlying adjustment for PA in studies of SB and a given outcome, and considers the implications for associations between SB and health.

No MeSH data available.