Advanced Jail Population Analysis: How to Retrospectively Analyze Average Daily Jail Subpopulations

• In Event: Carceral Surveillance and Population Monitoring: Tools, Tensions, and Impacts

Abstract

When a jail collects data on the average daily population (ADP) they create a daily snapshot of who is in the jail at a point in time. Snapshots typically include common breakdowns of subpopulations like gender, age, and pretrial status. Researchers, jail analysts, and policy organizations interested in more specific subpopulations rely on a standard approach in the literature that uses jail releases instead of calculating the subpopulations.

We specify a novel method using a sliding, dynamic window calculation written in Polars (a modern, performant dataframe library with Python bindings) that retroactively recalculates jail ADP. We demonstrate how the technique provides an improved understanding of compositional changes in Cook County’s Jail after the implementation of the Pretrial Fairness Act in Illinois. And demonstrate how reliance on release subpopulations biases the interpretation of jail composition and trends over time.

Author

• Branden Jaymes Dupont, Loyola University Chicago