Table 5.

Correlations^∗ of features with socioeconomic variables

Age		Gender		Education
Variable	Corr.†	Variable	Corr.‡	Variable	Corr.§
MFCC-3 kurtosis	−0.200	MFCC-10 kurtosis	−0.239	Preposition freq.	0.230
Conjunction freq.	0.182	MFCC-12 variance	0.181	Hapax legomena	0.222
Brunet's W index	0.179	MFCC-13 variance	0.179	Vocabulary size	0.219
General entropy	0.177	MFCC-5 skewness	0.175	Text size	0.207
Auxiliary verb freq.	0.175	MFCC-5 variance	0.174	General entropy	0.201
MFCC-1 variance	0.172	MFCC-8 skewness	−0.169	Adjective freq.	0.200
MFCC-6 kurtosis	−0.168	MFCC-10 skewness	0.163	Conjunction freq.	0.191
MFCC-5 kurtosis	−0.164			Noun freq.	0.190
MFCC-9 kurtosis	−0.158			Informativeness t = 60%	0.190
Informativeness score	0.156			Auxiliary verb freq.	0.184
				Verb freq.	0.172
				Informativeness score	0.169
				Brunet's W index	0.167

Abbreviations: Corr, correlation; MFCC, Mel-Frequency Cepstral Coefficient; freq., frequency.

^∗All correlations presented with P value < .001. Variables are shown in descending order with respect to the strength of their correlation.

^†Controlled for education, gender, and cognitive status.

^‡Controlled for age, education, and cognitive status.

^§Controlled for age, gender, and cognitive status.