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. 2021 Mar 31;50(3):975–986. doi: 10.1093/ije/dyab060

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© The Author(s) 2021. Published by Oxford University Press on behalf of the International Epidemiological Association.

This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs licence (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reproduction and distribution of the work, in any medium, provided the original work is not altered or transformed in any way, and that the work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

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Funnel plots of the risk of nasopharyngeal carcinoma (log-adjusted hazard ratios) associated with A: ever smokers; B: former smokers (both versus never) in the two-stage approach individual participant data meta-analysis (men only)