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. 2012 Apr 29;67(8):718–726. doi: 10.1136/thoraxjnl-2011-201445

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© 2012, Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

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Absolute change in forced expiratory volume in 1 s (FEV₁) in ml after bronchodilator (ΔFEV₁) expressed as 95th percentile with 95% CI in healthy non-smokers. Those sites whose estimates are most stable get greater weight (right-hand column) in constructing the pooled estimate of 284 ml. We observed significant heterogeneity across sites (p=0.008), with 54% of the overall variability in the data attributable to site–site variability.