Fig. 4From: 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 biases B1 and B2 are present. We set the risk ratio P(NFARI if healthy)/P(NFARI if frail) =0.75 and let the risk ratio R2 = P(FARI if healthy)/P(FARI if frail) vary between 0.5 to 1.0. The probabilities of vaccination are 0.8 and 0.4 for healthy and frail persons, respectivelyBack to article page