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. 2018 Apr 5;18(4):1101. doi: 10.3390/s18041101

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© 2018 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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Individual activity analysis of sum vector magnitude $J_{1}$ and standard deviation magnitude $J_{2}$ . The horizontal red line corresponds to the optimal threshold value, and the vertical one separates ADLs and falls. (a) $J_{1}$ has large errors on periodic activities (D1–D6, D18–D19); while (b) $J_{2}$ fails in those that change the body angle (D13, D14).