Table 1. Joint effect and interaction of low methylation and elderly age on the prognosis of early-stage lung adenocarcinoma (LUAD).

Effect type a	Elderly b	Low methylation	Number	Death	Crude mortality	HR (95% CI) a	Pa
	No	No	75	17	22.67%	Ref.
Main effect 1	No	Yes	70	33	47.14%	2.8398 (1.5876,5.0798)	4.35×10-4
Main effect 2	Yes	No	217	98	45.16%	3.1804 (1.8542,5.4553)	2.64×10-5
Joint effect	Yes	Yes	222	70	31.53%	1.8590 (1.0840,3.1890)	0.0242
Interaction c						0.2058 (0.1070,0.3961)	2.20×10-6

^a Patients categorized into two groups (low vs high) by medium of cg14326354_PRODH methylation level. Classification criteria of age were based on boundary of 95% confidence interval (CI) standard (young: <57 years; elderly >65 years).

^b Main effects of low methylation and elderly age and their joint effect and interaction were derived from Cox proportional hazards model adjusted for covariates.

^c Interaction = Joint effect ÷ (Main effect ₁ × Main effect ₂). 0.2058 ≈ 1.8590 ÷ (3.1804 × 2.8398).