Table 2.

Correlation between stress levels and speech features.

Top 10 features for each data set		Task	Spearman correlation
Female data set
	MFCCa3 acceleration skewness	Positive story	0.49
	MFCC2 mean	Neutral story	0.44
	Pitch range	Positive story	0.44
	MFCC3 acceleration skewness	Negative story	0.43
	MFCC2 mean	Positive story	0.44
	MFCC5 acceleration kurtosis	Negative story	–0.42
	MFCC2 mean	Negative story	0.43
	MFCC5 velocity kurtosis	Negative story	–0.40
	MFCC3 acceleration skewness	Neutral story	0.39
	MFCC5 velocity kurtosis	Negative story	0.39
Male data set
	Upper quartile F0b	Neutral story	–0.54
	Pronunciation posteriori probability score percentage	Positive story	–0.50
	Energy acceleration mean	Positive story	0.52
	Mean F0	Neutral story	–0.51
	MFCC9 kurtosis	Positive story	0.41
	MFCC9 variance	Positive story	–0.44
	Upper quartile F0	Negative story	–0.47
	MFCC4 acceleration mean	Positive story	–0.40
	Upper quartile F0	Positive story	–0.47
	MFCC12 acceleration skewness	Neutral story	–0.42

^aMFCC: mel-frequency cepstral coefficient; the numbers following MFCC are part of the feature names presenting their location on a spectrum.

^bF0: fundamental frequency.