# Break down why a number changed between two periods

A driver breakdown and bridge that shows exactly which segments, volume, price, or mix effects caused a metric to move.

- Topic: Data & Analysis
- Framework: Few-Shot
- Level: Advanced
- Tags: Analyze, Explain & Teach, Fill-in Template
- Source: https://www.thinkwithprompt.com/prompts/break-down-why-a-number-changed-between-two-periods

## Prompt

```text
Help me explain why a key number changed and which drivers caused it.

**Metric:** [e.g. revenue, gross margin, conversion rate, payroll cost, ticket volume]
**Periods compared:** [e.g. "Q3 vs. Q2", "this month vs. the same month last year"]
**Data for both periods:** [PASTE - broken down by whatever I have: product, region, channel, customer segment, price, volume]
**Known events:** [price changes, launches, outages, seasonality, one-offs, definition changes]
**Audience:** [WHO will hear the explanation]

Steps:
1. Calculate the total change in absolute and percentage terms.
2. Decompose it into drivers. For a rate or average, separate mix (the make-up of the base changed) from rate (performance within each segment changed). For revenue or cost, separate volume, price or rate, and mix. Make the parts add up exactly to the total.
3. Rank segments by their contribution to the total change, not by their own percentage change.
4. Separate one-off and timing effects from ongoing ones.
5. Flag any movement that could be a data or definition change rather than a real change.

Return:
1. A one-sentence answer: "[Metric] changed by [amount], mainly because ..."
2. A bridge table: Starting value | Each driver's contribution | Ending value, reconciling exactly. Describe how to show it as a waterfall chart in Excel or PowerPoint.
3. Top 5 contributors: Segment | Contribution | Explanation | Evidence | Confidence.
4. The unexplained remainder and what to check next.
5. A 3-bullet summary for my audience.

Use only my data. Where a driver is plausible but not shown in the data, label it [HYPOTHESIS - VERIFY] rather than stating it as the cause.
```

## What to fill in

- e.g. "Q3 vs. Q2", "this month vs. the same month last year"
- WHO will hear the explanation
- Metric
- amount
- HYPOTHESIS - VERIFY

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