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. 2019 Aug 7;74(9):875–881. doi: 10.1136/thoraxjnl-2018-212740

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© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY. Published by BMJ.

This is an open access article distributed in accordance with the Creative Commons Attribution 4.0 Unported (CC BY 4.0) license, which permits others to copy, redistribute, remix, transform and build upon this work for any purpose, provided the original work is properly cited, a link to the licence is given, and indication of whether changes were made. See: https://creativecommons.org/licenses/by/4.0/.

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Raw and fitted quit ratios from the (a) linear and best fitting (b) unsegmented and (c) segmented regression models. Red line, regression line; black dots, observed data; shaded grey areas, CIs of regression lines; 2BP, two break points.