Table 1.

Comparison of maximum phonation time.

	Intervention group				Control group
	n	MPT at first visit	MPT at 6 month	∆	n	MPT at first visit	MPT at 6 month	∆
Group A less than 5 seconds	11	3.3 ± 0.28	16 ± 2.57	12.6 ± 8.60	7	3.7 ± 0.18	8.4 ± 1.83	4.7 ± 5.26
Group B 5 to less than 10 seconds	60	6.8 ± 0.16	15.0 ± 0.76	8.2 ± 5.65	38	7.7 ± 0.18	10.1 ± 0.57	2.2 ± 3.50
Group C 10 to less than 15 seconds	70	11.9 ± 0.16	21.1 ± 0.87	9.1 ± 7.23	64	11.7 ± 0.17	13.0 ± 0.52	1.2 ± 3.86
Group D 15 to less than 20 seconds	38	16.4 ± 0.23	23.6 ± 1.07	7.1 ± 6.68	43	17.0 ± 0.41	16.4 ± 0.66	−0.6 ± 4.02
Group E 20 seconds and more	20	24.1 ± 0.83	29.9 ± 1.33	5.8 ± 5.73	57	24.7 ± 0.60	21.5 ± 0.87	−3.2 ± 6.30

MPT: maximum phonation time (seconds).

By the maximum phonation time levels of the first visit, we divided patients into five groups of A–E.

In all the five groups, there was a tendency that the maximum phonation time had been extended longer in the intervention groups than the control groups.