Table 3.

Odds of Idiopathic Pulmonary Fibrosis among Male Vietnam Veterans with Agent Orange Exposure versus No Agent Orange Exposure by Subgroup

	Odds Ratio (95% Confidence Interval)	P Value
Subgroups (adjusted)
Age at beginning of study period
Quartile 1: 53–60.1 yr old	1.15 (1.11–1.20)	<0.001
Quartile 2: 60.1–62.8 yr old	1.08 (1.04–1.11)	<0.001
Quartile 3: 62.8–66.3 yr old	1.06 (1.03–1.10)	<0.001
Quartile 4: 66.3–100 yr old	1.02 (0.97–1.06)	0.482
Tobacco use
Smoker	1.07 (1.05–1.09)	<0.001
Non-Smoker	1.13 (1.08–1.18)	<0.001

Owing to nonlinearity of variable age, age at the beginning of the study period (January 1, 2010) was subcategorized into equal quartiles. Adjusted multivariable regression controlled for idiopathic pulmonary fibrosis risk factors (age, race, ethnicity, smoking history, and rurality) and accounted for interactions between Agent Orange × age and Agent Orange × smoking in the model. The subgroup analysis compares risk of idiopathic pulmonary fibrosis among Veterans with Agent Orange exposure versus no Agent Orange exposure (reference group) for each interaction subgroup while holding other variables constant.