---
type: method
slug: measure-change-over-time
title: "Measure change over time correctly"
category: "Science & Data Analysis"
subcategory: "Data analysis"
level: starter
source: https://deepstoryresearch.com/method/measure-change-over-time
publisher: Deepstory Research
---

> **How to use this file:** attach it to ChatGPT, Claude, Gemini or Copilot (or paste the prompt section), replace every [PLACEHOLDER] with your details, and add any data or Deepstory evidence files the method needs.

## When to use this method
- Reporting growth, change or trends.

## Prompt

# Measure change over time correctly
Method by Deepstory Research: deepstoryresearch.com/method/measure-change-over-time

You are an official-statistics analyst. Follow the method below step by step. Goal: Start-to-end change, growth rates and CAGR computed correctly, with revision and base-effect warnings.

## My inputs
- Series: [SERIES]  (example: attach data)
- Start and end period: [START_AND_END_PERIOD]  (example: 2019 and 2024)
- Unit: [UNIT]  (example: % or currency)

Before you start: if any input above is still in [BRACKETS] or missing, ask me for it in one short numbered list and wait. Do not guess. If I attached files (data, briefs, Deepstory evidence files), treat them as the primary source.

## Steps to follow
1. Fix the endpoints and check both exist.
2. Compute absolute change, % change and CAGR (show formulas).
3. Distinguish percentage points from percent.
4. Check for revisions, breaks and base effects.
5. Describe what happened between endpoints only if data shows it.

## Deliver the output in this structure
- Calculations
- Plain-English statement
- Caveats

## Quality rules
- Never interpolate unobserved years.
- Inflation-adjust money series or say they are nominal.
- Label every number as FACT (with source and date), ESTIMATE (show the calculation) or ASSUMPTION.
- If a Deepstory evidence file is attached, use its figures as the reference values and cite its source references; tag claims that are not from it as [UNVERIFIED].
- End with: the 3 assumptions that matter most, what would change the answer, and the single best next step.

## Evidence you can attach
- Change in internet use, 2019–2024: https://deepstoryresearch.com/data/internet-use-change-2019-2024
- US Inflation & the Fed: https://deepstoryresearch.com/data/us-inflation-fed (AI context file: https://deepstoryresearch.com/context/us-inflation-fed.md)
- Internet use ranking: https://deepstoryresearch.com/data/internet-use-peer-ranking
- Income and internet use: https://deepstoryresearch.com/data/income-vs-internet-use

---
Deepstory methods are process guidance for AI tools. Review AI output before relying on it; legal, tax, medical and investment matters need a qualified professional.