Table 3.

Relationship of primary unassisted patency with combinations of randomized treatment assignment and baseline aspirin use

Type of Treatment Comparison	Subgroup	Hazard Ratio (95% Confidence Interval)
Observational comparisons
baseline aspirin use versus no baseline aspirin use	All patients	0.83 (0.68 to 1.01)
	Patients assigned to the placebo arm	0.73 (0.55 to 0.97)
	Patients assigned to the ERDP/ASA arm	0.90 (0.67 to 1.22)
Randomized comparisons
assignment to ERDP/ASA versus assignment to placebo	All patients	0.82 (0.68 to 0.99)
	Patients not taking aspirin at baseline	0.75 (0.59 to 0.96)
	Patients taking aspirin at baseline	0.89 (0.66 to 1.19)
Randomized/observational comparison
patients randomized to ERDP/ASA or receiving aspirin at baseline (“any aspirin”) versus patients randomized to placebo and not receiving aspirin at baseline (“no aspirin”)	—	0.75 (0.61 to 0.93)

Shown are HRs for the overall comparison and each subgroup of aspirin exposure in the observational trial (aspirin use vs. nonuse at baseline, first panel) and in the randomized trial (ERDP/ASA vs placebo, second panel) as well as a post hoc comparison of patients randomized to ERDP/ASA or receiving aspirin at baseline (“any aspirin”) vs. patients randomized to placebo and not receiving aspirin at baseline (“no aspirin”; third panel). The p-value for the overall observational comparison between aspirin users and nonusers was 0.06 (first panel), and for the overall comparison of randomized treatment groups was 0.036 (second panel). The HRs for the interaction term comparing the two randomized subgroups (ERDP/ASA vs placebo, first panel) did not differ significantly between aspirin users and nonusers in the observational trial (P = 0.42). Similarly, the HRs for the interaction term comparing the subgroups of aspirin users vs nonusers at baseline (second panel) did not differ significantly between the two randomized groups in the randomized trial (P = 0.42).