[OC] These two scatter plots have identical correlation coefficients. Here’s why one looks so much tighter.

Both datasets: r = 0.70. Same correlation coefficient. But one looks noticeably more clustered around the regression line. The difference is purely in the standard deviations – not the strength of the relationship. Because Pearson's r converts everything into standard units before measuring, it's blind to how physically spread out the data is. Smaller SDs [...]