Nowcasting Neighborhood Overdose Deaths in LA County

Thu, 10 Sep 2026 00:00:00 -0700

Overdose death records take 90–120 days to finalize, so public health teams are always looking at the past. As part of Rapid Overdose Surveillance Los Angeles (ROSLA), this project builds nowcasts of overdose mortality across Los Angeles County ZIP codes to close that gap.

Models. Gradient-boosted Poisson count models trained in a walk-forward backtest on finalized Medical Examiner records from 2012 to 2025, so every estimate uses only data that would have been available at the time.
Signals. Each neighborhood’s own overdose history is combined with public data: treatment-facility access, deprivation indices, homeless counts, drug-checking results, EMS calls, and search trends.
Knowing what’s knowable. When a ZIP code averages about one death per quarter, random chance dominates. The project measures the ceiling that counting noise places on any model, and uses it to choose the geography and time period where a real rise becomes detectable.

How well each approach identifies the 20 highest-burden ZIP codes, scored against realized counts (open) and against four-quarter deaths that smooth out counting noise (filled).

Manuscript in preparation.

gradient boosting | Fabrice Harel-Canada

Nowcasting Neighborhood Overdose Deaths in LA County