Table 1. Descriptions of 2000–2001 birth cohort who had undergone tympanostomy tubes before 9 years of age.

Characteristics	n	%
Total subjects	1755	100.0
Gender*
Male	1065	60.7
Female	689	39.3
Age at 1st tube insertion*
0–2 years	183	10.4
2–4 years	222	12.7
4–6 years	856	48.8
6–9 years	494	28.2
Number of chronic OME episodes
1	1627	92.7
2	111	6.3
3	12	0.7
4+	5	0.3
Surgical operation
Tube only	988	56.3
Tube + Adenoidectomy	767	43.7
Age at tube insertion†
1st tube insertion	5.0	1.8
2nd tube insertion	5.9	1.5
3rd tube insertion	6.9	1.3
Age at adenoidectomy‡
0–2 years	5	0.6
2–4 years	82	10.1
4–6 years	450	55.5
6–9 years	274	33.8

*One missing value.

^†Shown by mean and standard deviation.

^‡Only those who had undergone adenoidectomy were included (n = 767).