4. Significance of treatment‐effect modifiers for the relative treatment effect and absolute treatment effect for each of the subgroup variables.

Effect of surgery on the risk of the primary outcome (P value)
	Relative risk reduction		Absolute reduction in 5‐year actuarial risk
	Cox model	5‐year actuarial risk
Predefined participant subgroups
Sex	0.007	0.008	0.003
Age groups	0.09 0.05 (trend)	0.04	0.03
Time since last event groups	0.04 0.006 (trend)	0.05	0.009
Primary symptomatic event	0.21	0.30	0.16
Diabetes	0.51	0.85	0.63
Irregular or ulcerated plaque	0.58	0.23	0.10
Contralateral ICA occlusion	0.30	0.34	0.25
Post‐hoc participant subgroups
Duration of cerebral TIA	0.44	0.47	0.42
Previous TIA or stroke	0.08	0.23	0.50
Myocardial infarction	0.06	0.02	0.01
Angina	0.08	0.11	0.06
Treated hypertension	0.19	0.29	0.09
Treated hyperlipidaemia	0.63	0.85	0.85
Smoking	0.40	0.40	0.38

ICA: internal carotid artery
TIA: transient ischaemic attack