Table 5. Measures for estimation of synergic effect between tumor size and N stage for the risk of distant metastasis in DTC.

Tumor size	N stage	M1 case (%)	Total case	Odds ratio (95% CI)	P value
<10 mm	0	71 (0.3)	28,048	Reference
	1	53 (1.6)	3,274	7.807 (4.978–12.242)	<0.001*
≥10 mm	0	393 (0.9)	43,168	4.979 (3.553–6.978)	<0.001*
	1	579 (3.5)	16,689	13.584 (9.617–19.189)	<0.001*
RERI	5.058 (2.713–7.403)
AP	0.357 (0.219–0.496)
SI	1.624 (1.275–2.069)

Adjusted for age at diagnosis, sex, race, histology subtype, extrathyroidal extension. *, represent the P value <0.05. DTC, differentiated thyroid cancer; CI, confidence interval; RERI, relative excess risk; AP, attributable proportion; SI, synergy index.