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. 2016 Nov 17;90(2):207–216. doi: 10.1007/s00420-016-1186-7

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© The Author(s) 2016

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.

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Fig. 2 — Fraction of work (%) with different kinds of fuels used by clients from 1975 to 2010. *Wilcoxon signed rank test for the use of fuel by clients before/ after the year of 2000