Table 2. Mean formant frequencies of snoring in REM and NREM sleep according to gender

Sleep stage	Male				Female
	F1	F2	F3	F4	F1	F2	F3	F4
REM	838.63	1,747.85*	2,781.14	3,951.43	791.34	1,754.28	2,627.24	4,103.84
NREM	882.30	1,885.76*	2,933.08	4,114.79	691.14	1,844.82	2,627.50	4,058.48

Statistics: paired t-test, Wilcoxon signed-rank test.
p<0.05.
REM: rapid eye movement, NREM: non-rapid eye movement, F₁, F₂, F₃, F₄: first, second, third, and fourth formant frequencies (Hz).