Table 1. Demographic and pathological features of patients.

	n	%	Mean±df
Age (year)			59.6±8.3
Sex
Male	986	91.6
Female	91	8.4
Operation type
Lobectomy	741	68.8
Pneumonectomy	336	31.2
Histological type
Squamous cell carcinoma	623	57.8
Adenocarcinoma	411	38.2
Other	43	4.0
Tumor diameter (cm±df)			5.0±2.6
0-1	26
0-2	109
2-3	167
3-4	195
4-5	178
5-7	197
>7	205
PL0 (No pleural invasion)	773	71.8
PL1 (Invasion beyond the elastic layer)	64	5.9
PL2 (Invasion to the surface of the visceral pleura)	137	12.7
PL3 (Invasion of the parietal pleura)	103	9.6
df: Degree of freedom.