Table 3. Observable odds ratio (OR)^a, by sensitivity of birth certificate to identify prenatal smoking, the proportion of non-diseased who smoke, and true OR.

	Proportion non-diseased	True disease-smoking odds ratio
Sensitivity	who smoke	1.2	1.5	2.0	3.0	5.0
85%	0.10	1.18	1.44	1.87	2.72	4.33
	0.20	1.18	1.45	1.89	2.71	4.21
	0.30	1.18	1.44	1.86	2.63	3.93
79%	0.10	1.17	1.43	1.86	2.67	4.20
	0.20	1.18	1.44	1.86	2.64	4.00
	0.30	1.18	1.43	1.82	2.52	3.66
73%	0.10	1.17	1.42	1.84	2.63	4.08
	0.20	1.17	1.43	1.83	2.57	3.82
	0.30	1.17	1.41	1.78	2.43	3.44

^aAccording to the attenuation equation [30]. Assumes non-differential exposure measurement error (sensitivity equal in diseased and non-diseased, specificity = 99% in both diseased and non-diseased), and no error in outcome ascertainment.