Feature engineering and preprocessing · insight-0120

Guard ratio features against zero and tiny denominators

Situation
You build ratios such as revenue per seat, cancellations per booking or spend per visit.
Action
Define the ratio's behaviour for small denominators explicitly: add a floor, smooth with a prior, set to missing below a minimum count, and keep the denominator as its own feature.
Reason
A ratio from three bookings is far noisier than one from three hundred; keeping the denominator lets the model learn how much to trust it.
Boundary
Rates, per-unit metrics and conversion features in any tabular model.

Symptom or risk

Rows with near-zero denominators produce enormous or infinite values that dominate scaling, losses and plots.

Physically bounded ratios with large denominators, such as load factor on fixed capacity, are usually safe.

Floors and smoothing introduce bias for small groups in exchange for stability.

Computing a ratio from a numerator measured after the prediction time, such as final bookings on the day of departure.