(b) Constant time 0.5 s, P0.5
P0.5 sound parameter	Correlation with cough strength VAS
	Free-field microphone	Contact microphone
PW	0.88 (0.67 to 0.90)	0.83 (0.46 to 0.85)
Ep	0.77 (0.61 to 0.88)	0.68 (0.52 to 0.88)
RT	0.32 (−0.09 to 0.66)	0.44 (−0.02 to 0.71)
D	0.17 (0.00 to 0.31)	0.17 (0.00 to 0.31)
Fp	0.43 (0.21 to 0.65)	0.30 (0.00 to 0.64)
BW	0.03 (−0.62 to 0.32)	0.12 (−0.24 to 0.39)
Fc	0.34 (0.06 to 0.72)	0.66 (0.31 to 0.78)

Data are presented as median (IQR) within-subject Spearman's correlation coefficients between cough sound and cough strength VAS. Individual correlation coefficients are presented in online supplementary table 7. (PW, power; Ep, peak energy; RT, rise time; D, duration; Fp, peak frequency; BW, bandwidth; Fc, centroid frequency).