# Goodhart's Law

> Check how a metric could be gamed before you tie rewards to it.

Chapter I, Systems thinking · 1.09 · Origin: Charles Goodhart; phrased by Marilyn Strathern (1975) · Time: 20 to 40 min · Solo or group

**Use it when** you are about to set a target, a metric or an incentive.

Interactive workspace: https://kogu.tools/tools/goodharts-law

## Abstract

Once a number becomes a target, people find ways to move the number that don't move the thing it was supposed to track. Charles Goodhart noticed this in monetary policy in 1975, and the anthropologist Marilyn Strathern later gave it the wording most people quote: when a measure becomes a target, it ceases to be a good measure.

The best-known story is the cobra effect, where a bounty on dead cobras led people to breed cobras. This tool asks how your metric could be gamed and how likely each route is, then pairs each one with a second measure that would catch it.

## Method

1. **Start from the goal.** Write down, in plain words, the outcome you actually care about before you pick a number.
2. **Name the metric.** Write the measure you plan to use and what happens to people who hit or miss it.
3. **Imagine the gaming.** List the ways someone could hit the number without helping the goal. Picture a smart person under pressure to deliver.
4. **Pair the measures.** For each way of gaming it, add a second measure that would show it up, such as tracking quality alongside speed.
5. **Check and revise.** Go through the checklist, then write the revised plan, including when you'll review it.

## When to use it

- You're about to set targets or bonuses.
- A metric keeps improving while the thing you care about doesn't.
- You're designing a policy or reward that will change how people behave.

## Common pitfalls

- Assuming nobody will game it. Most gaming isn't cheating, just people responding sensibly to the incentive.
- Adding so many counter-metrics that nobody can tell which one to watch.
- Measuring what's easy to count instead of what's close to the goal.
- Never reviewing the metric. People get better at gaming a system the longer it runs.

## References

- Goodhart, C. A. E. (1975). Problems of monetary management: The U.K. experience. Papers in Monetary Economics, Reserve Bank of Australia.
- Strathern, M. (1997). 'Improving ratings': audit in the British university system. European Review, 5(3), 305 to 321.
- Campbell, D. T. (1979). Assessing the impact of planned social change. Evaluation and Program Planning, 2(1), 67 to 90.
- Grove, A. S. (1983). High Output Management. Random House.