Time-Dependent Confounding in the Study of the Effects of Regular Physical Activity in Chronic Obstructive Pulmonary Disease: An Application of the Marginal Structural Model.

TY - JOUR

T1 - Time-Dependent Confounding in the Study of the Effects of Regular Physical Activity in Chronic Obstructive Pulmonary Disease: An Application of the Marginal Structural Model.

AU - Garcia-Aymerich, J.

AU - Lange, P.

AU - Serra, I.

AU - Schnohr, P.

AU - Anto, J.M.

PY - 2008

Y1 - 2008

N2 - PURPOSE: Results from longitudinal studies about the association between physical activity and chronic obstructive pulmonary disease (COPD) may have been biased because they did not properly adjust for time-dependent confounders. Marginal structural models (MSMs) have been proposed to address this type of confounding. We sought to assess the presence of time-dependent confounding in the association between physical activity and COPD development and course by comparing risk estimates between standard statistical methods and MSMs. METHODS: By using the population-based cohort Copenhagen City Heart Study, 6,568 subjects selected from the general population in 1976 were followed up until 2004 with three repeated examinations. RESULTS: Moderate to high compared with low physical activity was associated with a reduced risk of developing COPD both in the standard analysis (odds ratio [OR] 0.76, p = 0.007) and in the MSM analysis (OR 0.79, p = 0.025). In the subgroup with COPD (n = 2,226), high physical activity was associated with a reduced risk of COPD admissions during follow-up (standard, incidence rate ratio, 0.74; p = 0.096; MSM, 0.68, p = 0.044), and with a reduced risk of mortality (standard, hazard ratio 0.80, p = 0.001; MSM, 0.81, p = 0.008). CONCLUSION: These results support the previously reported associations between physical activity and reduced risk of COPD development, hospitalizations, and mortality, thereby suggesting they were not due to time-dependent confounding.

AB - PURPOSE: Results from longitudinal studies about the association between physical activity and chronic obstructive pulmonary disease (COPD) may have been biased because they did not properly adjust for time-dependent confounders. Marginal structural models (MSMs) have been proposed to address this type of confounding. We sought to assess the presence of time-dependent confounding in the association between physical activity and COPD development and course by comparing risk estimates between standard statistical methods and MSMs. METHODS: By using the population-based cohort Copenhagen City Heart Study, 6,568 subjects selected from the general population in 1976 were followed up until 2004 with three repeated examinations. RESULTS: Moderate to high compared with low physical activity was associated with a reduced risk of developing COPD both in the standard analysis (odds ratio [OR] 0.76, p = 0.007) and in the MSM analysis (OR 0.79, p = 0.025). In the subgroup with COPD (n = 2,226), high physical activity was associated with a reduced risk of COPD admissions during follow-up (standard, incidence rate ratio, 0.74; p = 0.096; MSM, 0.68, p = 0.044), and with a reduced risk of mortality (standard, hazard ratio 0.80, p = 0.001; MSM, 0.81, p = 0.008). CONCLUSION: These results support the previously reported associations between physical activity and reduced risk of COPD development, hospitalizations, and mortality, thereby suggesting they were not due to time-dependent confounding.

U2 - http://dx.doi.org/10.1016/j.annepidem.2008.05.003

DO - http://dx.doi.org/10.1016/j.annepidem.2008.05.003

M3 - Journal article

SN - 1047-2797

VL - 18

SP - 775

EP - 783

JO - Annals of Epidemiology

JF - Annals of Epidemiology

IS - 10

ER -