Table 1. Power of the likelihood ratio tests* for interaction.

Case-control ratio	Sampling method
	Matched	Counter-matched	Unmatched
		Additive model
1:1	0.26	0.36	0.20
1:2	0.39	2 unexposed, 1 exposed: 0.45	0.33
		1 unexposed, 2 exposed: 0.35
1:3	0.62	0.94	0.38
1:5	0.72	0.94	0.39
1:9	0.95	1.00	0.71
		Multiplicative model
1:1	0.01	0.02	0.06
1:2	0.02	2 unexposed, 1 exposed: 0.00	0.03
		1 unexposed, 2 exposed: 0.02
1:3	0.00	0.00	0.00
1:5	0.00	0.00	0.01
1:9	0.00	0.00	0.00

* Test size (probability of rejection given the null hypothesis of no interaction) was 0.05.