Key result
In patients with asthma or COPD, ever-use of long-acting beta-agonists was not associated with increased all-cause mortality after full adjustment for confounding variables (RR 0.98).
Why the study?
Does ever use of inhaled long-acting beta-agonists (LABA) affect all-cause mortality in patients with asthma or COPD?
Observational (n=2,394)
Does ever use of inhaled long-acting beta-agonists (LABA) affect all-cause mortality in patients with asthma or COPD?
Answers are grounded in this paper and cite their sources.
This methodological study demonstrates that confounding variables should not be discarded based on balanced baseline distributions, as residual confounding can still occur when adjusting for other variables.
In observational studies, selection of confounding variables for adjustment is often based on observed baseline incomparability. The aim of this study was to evaluate this selection strategy. We used clinical data on the effects of inhaled long-acting beta-agonist (LABA) use on the risk of mortality among patients with obstructive pulmonary disease to illustrate the impact of selection of confounding variables for adjustment based on baseline comparisons. Among 2,394 asthma and COPD patients included in the analyses, the LABA ever-users were considerably older than never-users, but cardiovascular co-morbidity was equally prevalent (19.9% vs. 19.9%). Adjustment for cardiovascular co-morbidity status did not affect the crude risk ratio (RR) for mortality: crude RR 1.19 (95% CI 0.93–1.51) versus RR 1.19 (95% CI 0.94–1.50) after adjustment for cardiovascular co-morbidity. However, after adjustment for age (RR 0.95, 95% CI 0.76–1.19), additional adjustment for cardiovascular co-morbidity status did affect the association between LABA use and mortality (RR 1.01, 95% CI 0.80–1.26). Confounding variables should not be discarded based on balanced distributions among exposure groups, because residual confounding due to the omission of confounding variables from the adjustment model can be relevant.
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Groenwold et al. (2011) conducted an observational in Asthma and COPD (n=2,394). Inhaled long-acting beta-agonist (LABA) vs. Never LABA-users was evaluated on All-cause mortality (RR 0.98, 95% CI 0.79-1.23). In patients with asthma or COPD, ever-use of long-acting beta-agonists was not associated with increased all-cause mortality after full adjustment for confounding variables (RR 0.98).
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