Table 3. Tracheal index by age and gender .

-	n	Tracheal index mean ± SD (median) day 0-2	Tracheal index mean ± SD (median) day 15-30	p
Girls	71	1.84±0.30 (1.85)	1.99±0.23 (1.99)	<0.01
Boys	73	1.82±0.27 (1.82)	2.00±0.28 (1.90)	<0.01
Total	144	1.83±0.29 (1.82)	1.99±0.25 (1.94)	<0.01

The tracheal index is calculated as the ratio of the sum of the maximum widths of the right and left thyroid lobes in the transverse section to the width of the trachea at the thyroid level.

SD: standard deviation