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Percentile

As explained in Machine Learning System Design

A value that divides a probability distribution so that a specified proportion of its mass lies at or below the value.

A percentile marks a chosen position in a distribution: a 95th percentile represents a forecast target associated with a 95% service level. In demand forecasting, choosing the right percentile is a business decision because higher coverage can reduce out-of-stocks while affecting inventory and forecast evaluation. section 5.3.1

Demand-forecasting baseline

A grocery retailer can calculate 1.5th, 25th, 50th, 75th, 95th, and 99th percentiles from a yearly window and apply them to a baseline forecast. A linear model can also use quantile loss with sales lags, rolling aggregates, price, revenue, or customer counts. The selected percentiles can be weighted by SKU price and adjusted when underforecasting or overforecasting has different costs. section 8.6.1 section 5.3.1

Percentiles connect forecast quality to operations rather than treating every error equally. Quantile forecasts can feed stock-control strategies, while quantile metrics can be reported with confidence intervals and compared across products or groups. section 5.3.1

How Machine Learning System Design covers it

How deep it goes
Explains percentile selection through forecast metrics, weighting, penalties, and baseline construction without deriving the underlying mathematics.
Examples
Uses yearly-window baseline percentiles, quantile-loss regression, rolling aggregates, SKU-price weights, and asymmetric forecast penalties.
What it assumes
Assumes basic forecasting and inventory context while connecting percentile choices to service levels and forecast errors.
What you can do after
Apply percentiles through quantile forecasts and metrics to compare baselines and align demand predictions with inventory priorities.
How it connects
Connects quantiles with predictive distributions, loss functions, scoring rules, stock control, forecasting, and service-level agreements.

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This explainer was generated by Manning's knowledge graph from the text of Machine Learning System Design. The section links point to the parts of the book it draws on.