Fig. 6From: A comparison of the test-negative and the traditional case-control study designs for estimation of influenza vaccine effectiveness under nonrandom vaccinationTrue and estimated VEs when only bias D is present as function of R4 = P(seeking medical care if healthy)/P(seeking medical care if frail). Probabilities of vaccination are 0.8 and 0.4 for healthy and frail persons, respectivelyBack to article page