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. 2021 Nov 2;11(11):e048013. doi: 10.1136/bmjopen-2020-048013

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© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

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Studies returned from systematic review of the published and grey literature. Step 1 involved screening of titles and abstracts only and step 2 the screening of full-text items not excluded at step 1 (see online supplemental tables 2 and 3). ‘Items’ are individual articles or reports, with multiple items returned for some studies (the purpose was to identify studies with suitable individual participant (IPD)-level data). *Mednar items with insufficient information available to review; **additional studies identified through known contacts; ***screening criteria for five items selected as ‘Maybe’ in step 2 were further investigated using information external to systematic searches and screenings, resulting in the identification of one additional study with suitable IPD-level data.