Judge whether a spike in daily counts is real with a Poisson check

Support tickets jumped yesterday, and I need to know if that's a real problem or just an ordinary busy day.

IntermediateRead 5 minDoing: 30 minutes6 steps

▶ Start

What you'll have at the end

A yes-or-no answer on whether yesterday's count was outside the normal range for that day of week

Before you start

You need

A day-by-day count of one recurring thing, like tickets, orders, or signups, covering at least eight past occurrences of the same weekday, plus yesterday's actual count for that same weekday.

Not covered

Working out why a real spike happened, or wiring this check into a dashboard that runs it automatically every day.

Leans on

Statistics Fundamentals Cheat Sheetthe Poisson and p-value rows carry the two ideas this whole check leans on.
Data Visualization for BI Cheat Sheetthe calendar heatmap row is the fastest way to show a manager the pattern behind today's call.

6 steps

Where to go next

Replace hourly KPI checking with one threshold alert

once this check needs to run every day instead of once, wire the same boundary into an automatic alert rather than recomputing it by hand each morning

Checked 26 Aug 2026

Part of the Statistics Fundamentals cookbook