Table 3.

Leave-one-out classification rate of the signal quality indices ranked in descending order. Four classification methods are used in this analysis: Mahalanobis distance, linear discriminant analysis (LDA), quadratic discriminant analysis (QDA), and the linear support vector machine (SVM). Eight SQIs are tested: perfusion (${\mathrm{P}}_{\mathrm{SQI}}$), kurtosis (${\mathrm{K}}_{\mathrm{SQI}}$), skewness (${\mathrm{S}}_{\mathrm{SQI}}$), relative power (${\mathrm{R}}_{\mathrm{SQI}}$), non-stationarity (${\mathrm{N}}_{\mathrm{SQI}}$), zero crossing (${\mathrm{Z}}_{\mathrm{SQI}}$), entropy (${\mathrm{E}}_{\mathrm{SQI}}$), and the matching of systolic wave detectors (${\mathrm{M}}_{\mathrm{SQI}}$). The $F_1$ value of discriminating between excellent signal quality (G1), acceptable signal quality (G2), and unfit to diagnose signals (G3) is given in the last column of each comparison. Here, SE stands for sensitivity, PP stands for positive predictivity, $F_1$ stands for $F_1$ score accuracy test, OF stands for overall $F_1$ of all classifiers (average of all $F_1$), and NaN stands for not a number.

G1 ($\mathit{n}=36$) vs. G2 ($\mathit{n}=52$)
	Mahalanobis			LDA			QDA			SVM			Overall
Index	SE	PP	${\mathit{F}}_{\mathbf{1}}$	SE	PP	${\mathit{F}}_{\mathbf{1}}$	SE	PP	${\mathit{F}}_{\mathbf{1}}$	SE	PP	${\mathit{F}}_{\mathbf{1}}$	OF
${\mathrm{S}}_{\mathrm{SQI}}$	83.33	73.17	77.92	80.56	74.36	77.33	80.56	74.36	77.33	80.56	74.36	77.33	77.60
${\mathrm{M}}_{\mathrm{SQI}}$	83.33	46.88	60.00	83.33	46.15	59.41	83.33	43.48	57.14	88.89	45.07	59.81	63.07
${\mathrm{Z}}_{\mathrm{SQI}}$	80.56	42.03	55.24	83.33	42.86	56.60	88.89	41.03	56.14	94.44	42.50	58.62	61.85
${\mathrm{K}}_{\mathrm{SQI}}$	63.89	46.94	54.12	55.56	55.56	55.56	38.89	70.00	50.00	55.56	57.14	56.34	54.96
${\mathrm{P}}_{\mathrm{SQI}}$	47.22	39.53	43.04	66.67	48.00	55.81	66.67	36.92	47.52	83.33	41.10	55.05	52.57
${\mathrm{E}}_{\mathrm{SQI}}$	11.11	66.67	19.05	30.56	44.00	36.07	86.11	51.67	64.58	13.89	31.25	19.23	39.51
${\mathrm{R}}_{\mathrm{SQI}}$	5.56	100.00	10.53	19.44	50.00	28.00	91.67	41.25	56.90	8.33	37.50	13.64	38.57
${\mathrm{N}}_{\mathrm{SQI}}$	0.00	0.00	NaN	27.78	47.62	35.09	86.11	41.33	55.86	11.11	40.00	17.39	NaN
G1 ($\mathit{n}=\mathbf{36}$) vs. (G2 [$\mathit{n}=\mathbf{52}$] & G3 [$\mathit{n}=\mathbf{18}$])
	Mahalanobis			LDA			QDA			SVM			Overall
Index	SE	PP	${\mathit{F}}_{\mathbf{1}}$	SE	PP	${\mathit{F}}_{\mathbf{1}}$	SE	PP	${\mathit{F}}_{\mathbf{1}}$	SE	PP	${\mathit{F}}_{\mathbf{1}}$	OF
${\mathrm{S}}_{\mathrm{SQI}}$	80.56	69.05	74.36	80.56	69.05	74.36	80.56	69.05	74.36	80.56	69.05	74.36	74.65
${\mathrm{M}}_{\mathrm{SQI}}$	83.33	40.00	54.05	83.33	39.47	53.57	83.33	37.50	51.72	88.89	38.10	53.33	58.89
${\mathrm{Z}}_{\mathrm{SQI}}$	83.33	37.50	51.72	86.11	37.35	52.10	88.89	35.16	50.39	94.44	35.79	51.91	58.73
${\mathrm{P}}_{\mathrm{SQI}}$	47.22	33.33	39.08	66.67	41.38	51.06	83.33	37.50	51.72	80.56	36.71	50.43	51.58
${\mathrm{N}}_{\mathrm{SQI}}$	5.56	100.00	10.53	72.22	30.95	43.33	86.11	34.07	48.82	94.44	33.01	48.92	50.66
${\mathrm{R}}_{\mathrm{SQI}}$	11.11	33.33	16.67	75.00	32.53	45.38	88.89	34.78	50.00	94.44	35.05	51.13	47.36
${\mathrm{K}}_{\mathrm{SQI}}$	44.44	37.21	40.51	47.22	41.46	44.16	22.22	40.00	28.57	36.11	44.83	40.00	38.89
${\mathrm{E}}_{\mathrm{SQI}}$	2.78	100.00	5.41	25.00	12.33	16.51	88.89	42.67	57.66	27.78	12.50	17.24	34.06
G1 ($\mathit{n}=\mathbf{36}$ ) vs. G3 ( $\mathit{n}=\mathbf{18}$)
	Mahalanobis			LDA			QDA			SVM			Overall
Index	SE	PP	${\mathit{F}}_{\mathbf{1}}$	SE	PP	${\mathit{F}}_{\mathbf{1}}$	SE	PP	${\mathit{F}}_{\mathbf{1}}$	SE	PP	${\mathit{F}}_{\mathbf{1}}$	OF
${\mathrm{S}}_{\mathrm{SQI}}$	77.78	93.33	84.85	80.56	90.63	85.29	83.33	90.91	86.96	77.78	93.33	84.85	85.80
${\mathrm{Z}}_{\mathrm{SQI}}$	86.11	73.81	79.49	88.89	72.73	80.00	88.89	71.11	79.01	88.89	72.73	80.00	80.14
${\mathrm{M}}_{\mathrm{SQI}}$	83.33	73.17	77.92	83.33	73.17	77.92	83.33	71.43	76.92	88.89	71.11	79.01	78.30
${\mathrm{E}}_{\mathrm{SQI}}$	72.22	76.47	74.29	80.56	74.36	77.33	88.89	71.11	79.01	88.89	71.11	79.01	77.77
${\mathrm{R}}_{\mathrm{SQI}}$	75.00	69.23	72.00	77.78	68.29	72.73	88.89	71.11	79.01	91.67	71.74	80.49	76.49
${\mathrm{P}}_{\mathrm{SQI}}$	66.67	72.73	69.57	77.78	75.68	76.71	83.33	75.00	78.95	83.33	75.00	78.95	76.14
${\mathrm{N}}_{\mathrm{SQI}}$	47.22	77.27	58.62	86.11	72.09	78.48	86.11	67.39	75.61	94.44	68.00	79.07	74.20
${\mathrm{K}}_{\mathrm{SQI}}$	72.22	74.29	73.24	72.22	76.47	74.29	75.00	71.05	72.97	72.22	76.47	74.29	73.73