Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
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 when the cumulative exposure effect model (4), RS covariance of the response, CS covariance of exposure, constant exposure prevalence and ρb0,b1 = −0.5 are assumed, for several values of r, ρt0, ρb1 and ρe. Y-axis on logarithmic scale. Lines indicate: (—) ρe = 0, (- - -) ρe = 0.5, (…) ρe = 1.
