Work out data drift (psi) instantly with clear inputs, formula shown and shareable results.
The Population Stability Index sums (actual - expected) x ln(actual / expected) over the bins of a feature, which is a symmetrised relative-entropy measure. Each bin's contribution is positive whether the share rose or fell, so the total grows with any redistribution. The industry convention is that below 0.1 is stable, 0.1 to 0.25 warrants monitoring and above 0.25 signals a material shift.
PSI
PSI = sum over bins of (actual% - expected%) x ln(actual% / expected%)
Use deciles of the baseline distribution so each expected share is 10 percent. Equal-width bins on a skewed feature put almost everything in one bin and hide real drift.
The logarithm is undefined, so implementations substitute a small floor such as 0.0001. Report that you have done so, because the PSI value becomes sensitive to that choice.