# Testing for confounding

Suppose we want to test whether $Z$ is a confounding variable for the effect of $X$ on $Y$. Is it enough to just check unadjusted and adjusted estimates of the coefficient of $X$ and see if they differ? Also, if the difference between the two is very small (e.g $1/1000$) can we say that there is no confounding? It seems in survival analysis it would be complicated to check for the association of $Z$ vs. $X$ and $Z$ vs. $Y$.