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. 2020 Feb 15;20:57. doi: 10.1186/s12883-020-01633-3

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© The Author(s) 2020

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Fig. 6 — Random-effect model of trial sequential analysis for changes in monthly migraine days. The dashed red lines represent the trial sequential monitoring boundary (upper O’Brien Fleming with α = 5%, β = 20%, low risk of bias). Required information size (RIS) of 506 participants were calculated. Complete blue line represents cumulative Z-curve, which is well past the RIS needed. Cumulative Z-curve cross conventional boundary (complete red line) and the trial sequential monitoring boundary (dashed red line)