Table 1.

Features derived from smartphone sensor signals. Acceleration due to gravity = (Xgrav, Ygrav, Zgrav), linear acceleration = (Xlin, Ylin, Zlin), SD = standard deviation

Signal Feature	Formula	Abbreviation
Simple moving average of sum of range of linear acceleration (4 windows)	$\frac{{{\Sigma }^4}_{\mathrm{i}=1}\left[\left(\mathit{range}\left(Xli{n}_i\right)\right)\pm \left(\mathit{range}\left(Yli{n}_i\right)\right)\pm \left(\mathit{range}\left(Zli{n}_i\right)\right)\right]}{4}$	L-SMA
Difference to Y	Ygrav–Zgrav–Xgrav	DifftoY
Sum of range of linear acceleration	(range(Xlin i)) + (range(Ylin i)) + (range(Zlin i))	SOR
Sum of standard deviation of linear acceleration	(SD(Xlin i)) + (SD(Ylin i)) + (SD(Zlin i))	SoSD
Maximum slope of simple moving average of sum of variances of gravity	$\frac{SM{A}_{var}={{\Sigma }^4}_{\mathrm{i}=1}\left(Var{\left(\mathit{Xgrav}\right)}_i\pm Var{\left(\mathit{Ygrav}\right)}_i\pm Var{\left(\mathit{Zgrav}\right)}_i\right)}{4}$ max(SMA var(2)–SMA var(1), SMA var(3)–SMA var(2), SMA var(4)–SMA var(3))	G-SMAvar