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. 2017 Mar 1;15:44. doi: 10.1186/s12955-017-0618-8

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© The Author(s). 2017

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. 1 — Graphical representation of the item response theory (IRT) for the GLLRM model. Item response theory (IRT) graph showing the relationships between items (CG1-5), independence (green), and background variables (grey). The arrows and edges between the covariates indicate that these variables are statistically associated. The IRT graph includes information on local dependence (e.g., line between CG1 and CG3), differential item functioning (DIF) (e.g., arrow between age and CG5), and the effect of background variables on independence (e.g., arrow between HbA1c), age, sex, and independence). Whereas time and treatment do not display any DIF or effect on independence