Figure 2.

 Pooled standardised mean difference of change in lung function 60 minutes after addition of unique (single dose protocol) or last (multiple dose protocol) anticholinergic treatment to β₂ agonists. Standardised mean difference, displayed on SD unit, represents difference in mean between groups relative to pooled SD of treatment and control groups. Studies reporting change in spirometry as percentage change in FEV₁ or change in percentage predicted FEV₁ were pooled while the trial reporting change in respiratory resistance is reported separately. Trials stratified according to concomitant administration of systemic corticosteroids. Width of horizontal line represents 95% confidence interval around point estimate (black square). Size of point estimate represents relative weight (% weight) of each trial in the pooled summary estimate (diamond). Vertical line is line of no effect (relative risk 0.0)