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. 2019 Apr 15;4(1):e000262. doi: 10.1136/tsaco-2018-000262

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© Author(s) (or their employer(s)) 2019. 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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Different methodologies used by each study (not mentioned=4 (3.8%), meta-analysis=1 (0.9%), poster/abstract=2 (1.9%), protocol=3 (2.8%), literature review=14 (13.3%), descriptive study=7 (6.6%), systematic review=4 (3.8%), retrospective review=18 (17%), case report=13 (12.3%), prospective observational study=10 (9.5%).