Table 5.

Interaction analysis of use of treatment vs no treatment for each period

Interaction analysis	Period 1999–2005 HR (95% CI)	Period 2006–2010 HR (95% CI)	Period 2011–2014 HR (95% CI)
Surgery, yes vs no	0.86 (0.81–0.91)	0.64 (0.60–0.68)	0.69 (0.64–0.74)
Radiotherapy, yes vs no	0.91 (0.86–0.97)	0.88 (0.83–0.94)	0.83 (0.77–0.89)
Chemotherapy, yes vs no	0.75 (0.70–0.80)	0.72 (0.68–0.76)	0.66 (0.61–0.70)

For the analysis, Cox Model 3 was used with the additional inclusion of all three interaction terms (treatment modalities × time period). Abbreviations: HR—hazard ratio, CI—confidence interval