Table 4. Multivariate analysis and the IPTW method using the propensity score for postoperative recurrence with spontaneous pneumothorax.

Factors	Multivariate analysis				IPTW method
	HR	95% CI	P value		HR	95% CI	P value
Type of SP: secondary	0.366	0.081–0.65	0.190		0.640	0.048–6.24	>0.99
Smoking habits: ever	0.507	0.197–1.31	0.161		0.163	0.003–1.85	0.149
Laterality of SP: left	1.09	0.508–2.34	0.822		1.91	0.196–25.3	0.646
Surgical approach: thoracoscopic surgery	2.63	0.538–12.8	0.232				N/A
Surgeon: resident	1.52	0.693–3.35	0.294		4.78	0.472–65.7	0.116
Operative time: >100 min	0.706	0.323–1.54	0.382		0.707	0.054–6.90	>0.99
Age: <30 years	6.54	1.340–32.1	0.021		14.3	1.21–783	0.015

HR, hazard ratio; IPTW, inverse probability of treatment-weighted; SP, spontaneous pneumothorax.