Numerical simulation (∼1000 points) that shows the impact of a big error (comparable with the variance of the variable, in this example Y) on the Y – X correlation. In this example we assume a correlation coefficient r ∼ 0.87 (lower panel) and we add an error on Y comparable with the intrinsic variance on Y. The resulting correlation (upper panel) is significantly reduced (r ∼ 0.62).