Limits...
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 confounder and intermediary between sedentary behaviour and disease outcomes. Sub-scripts denote measurement at time 1 and time 2.
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig3: Physical activity as a confounder and intermediary between sedentary behaviour and disease outcomes. Sub-scripts denote measurement at time 1 and time 2.

Mentions: Additionally, studies usually do not explicitly delineate the temporal ordering of SB and PA measures, and do not analytically address the inter-dependence of SB and PA across time: SB is a time-dependent exposure that is analysed in the presence of the time-dependent co-variate of PA. In this context, PA can be considered as both a confounder and an intermediary, where PA is an effect of SB but is also a common cause of SB and D (Figure 3). If conceptualising PA as a time-dependent co-variate of SB (a time-dependent exposure) is a more appropriate reflection of the putative aetiological mechanisms by which PA and SB affect health outcomes, then marginal structural models (MSMs) [16] can be used to estimate the ‘independent’ effects of SB on a given health outcome. MSMs provide a solution to the collider stratification bias inherent in conditional approaches to adjustment for PA in studies of SB and a given outcome (Figure 2). MSMs derive inverse probability weights to re-weight a dataset to reflect the probability of a given level of PA based on observed level of SB. This approach allows unbiased estimation of the marginal association between SB and D, adjusting for PA.Figure 3


Adjustment for physical activity in studies of sedentary behaviour.

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

Physical activity as a confounder and intermediary between sedentary behaviour and disease outcomes. Sub-scripts denote measurement at time 1 and time 2.
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig3: Physical activity as a confounder and intermediary between sedentary behaviour and disease outcomes. Sub-scripts denote measurement at time 1 and time 2.
Mentions: Additionally, studies usually do not explicitly delineate the temporal ordering of SB and PA measures, and do not analytically address the inter-dependence of SB and PA across time: SB is a time-dependent exposure that is analysed in the presence of the time-dependent co-variate of PA. In this context, PA can be considered as both a confounder and an intermediary, where PA is an effect of SB but is also a common cause of SB and D (Figure 3). If conceptualising PA as a time-dependent co-variate of SB (a time-dependent exposure) is a more appropriate reflection of the putative aetiological mechanisms by which PA and SB affect health outcomes, then marginal structural models (MSMs) [16] can be used to estimate the ‘independent’ effects of SB on a given health outcome. MSMs provide a solution to the collider stratification bias inherent in conditional approaches to adjustment for PA in studies of SB and a given outcome (Figure 2). MSMs derive inverse probability weights to re-weight a dataset to reflect the probability of a given level of PA based on observed level of SB. This approach allows unbiased estimation of the marginal association between SB and D, adjusting for PA.Figure 3

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.