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Sample size ratio (SSR = Nρe/Nρe=1) comparing the required sample size of a study with time-varying exposure to a study with time-invariant exposure under the acute exposure effect model (5), RS covariance of the response, CS covariance of exposure, constant exposure prevalence, V (t0) = 0 and ρb0,b1 = −0.5 are assumed, for several values of r,ρ, θ and ρe. Y-axis on logarithmic scale. Lines indicate: (—) ρe = 0, (- - -) ρe = 0.5, (…) ρe = 1.
