Goodhart's Law

Overview

Goodhart's Law: when a metric controls behavior, people optimize the metric rather than the underlying goal. Formulated by economist Charles Goodhart (1975) on UK monetary policy; sharpened by Marilyn Strathern (1997): "When a measure becomes a target, it ceases to be a good measure." Four failure mechanisms (Manheim & Garrabrant 2018): Regressional, Extremal, Causal, Adversarial. Countermeasure is always multi-metric + audit + rotation.

Composes with feedback-loops, principal-agent, okr-goal-setting, survivorship-bias.

When to Use

A KPI is being introduced or its weight is increasing in performance evaluation
A metric is "improving" without corresponding improvement in the underlying goal
People are visibly optimizing for a number rather than the work it was meant to track
Algorithmic optimization is producing outcomes the designers didn't intend
Resource allocation is driven by a single composite score or ranking

Not when: metric and goal are identical; stakes too low for gaming; metric is purely descriptive with no reward/punishment; question is which metric to use, not whether the measurement-reward system is sound.

Coaching Novices (Adaptive Front Door)

Engine mode: user has a concrete metric or system → run The Process directly.
Coach mode: user is unfamiliar or has no concrete case → guide step by step.

In Coach mode, respond one step at a time. Each [WAIT] is a hard stop — output only that step's question, then stop.

One-line: before relying on a metric to control behavior, predict how people will game it — choose the system that survives that prediction.
Check fit: if the metric is purely descriptive (no reward attached), Goodhart's law doesn't apply yet.
Elicit the specific metric and the underlying goal: what's being measured? What's the actual outcome you care about?

[WAIT — do not advance until user responds]

One question at a time: proxy gap? How would a clever agent game this? Which Goodhart category? What countermeasure fits?

[WAIT — do not advance until user responds]

Close: name the gaming-resistant design (multi-metric, audit, rotation, paired-constraint) + monitoring schedule.

[WAIT — do not advance until user responds]

The Process

Step 1 — State metric and goal: metric being targeted / underlying goal / current proxy-goal correlation / who is measured / stakes.

Step 2 — Predict the gaming: list ≥3 ways to game the metric with minimum effort on the goal. If you can't list 3, you haven't thought hard enough.

Step 3 — Categorize mechanism:

| Mechanism | Test | |---|---| | Regressional | Is there noise that optimization will push into? | | Extremal | Does metric-goal correlation break at extremes? | | Causal | Is the metric a symptom, not a cause? | | Adversarial | Will agents actively game with intelligence? |

Step 4 — Choose countermeasure: Regressional → constrain range. Extremal → paired constraint metrics. Causal → closer-to-causation metric + direct audit. Adversarial → multi-metric + randomized audits + rotation. Step 5 — Design the system: primary metric / constraint metric(s) / audit mechanism (sampled direct goal observation) / rotation schedule / separation of measure-for-control from measure-for-diagnosis / gaming-detection threshold. Step 6 — Schedule re-evaluation: independent goal measurement (how/when/who) / drift threshold / retirement criteria / owner.

Output template

# Goodhart-Robust Design: <metric>
Metric: | Underlying goal: | Correlation: | Who measured: | Stakes:
Gaming vectors (≥3):
Mechanism: Regressional / Extremal / Causal / Adversarial
Primary metric: | Constraint metric(s): | Audit: | Rotation: | Separation: | Gaming threshold:
Goal measurement (independent): | Drift threshold: | Retirement criteria: | Owner:

→ Method in Action: Goodhart 1975 (M3) and Strathern 1997 (RAE)

Pack: Goodhart's Law Patterns

| Domain | Common gaming | Defense | |---|---|---| | Sales quotas | Sandbagging, channel stuffing, end-of-quarter discounts | Multi-period averaging; quality metrics; clawback | | Hospital wait targets | Ambulance parking, patient reclassification | Outcome audits; paired metrics; randomized inspection | | Standardized testing | Teaching to test, curriculum narrowing | Sample-based assessment; multi-measure; reduce single-test stakes | | Algorithmic engagement | Clickbait, outrage, misinformation | Multi-objective optimization; quality + harm constraints |

Applying It Well

All metrics are proxies — narrower than the goal. Pre-commit to gap analysis before deployment.
Gaming is rational under measurement pressure. Fix the system, not the people.
Rotation and audit are the only durable defenses. Plan metric retirement at design time.

→ Primary sources: references/sources.md

Common Rationalizations

| Fake move | Reality | |---|---| | [D] "If you can't measure it, you can't manage it" | Often false. Judgment, trust, and direct observation are also valid management tools. | | [D] "Our metric is well-defined; it won't be gamed" | Precision invites precise gaming. Basel II capital ratios were well-defined — extensively gamed. | | [D] "Our people wouldn't game the metric" | Goodhart's law is structural; individual virtue is insufficient in aggregate. | | [D] "We just need a better metric" | Often the issue is any single metric under pressure; fix is multi-metric + audit. | | [D] "We've used this metric for years" | Long use = more time for gaming to mature. Tenure is a warning, not an endorsement. | | → Add [O] entries here after each real use — paste the actual failure pattern | What went wrong and why |

[D] = designed upfront | [O] = observed in real use. [O] entries are more valuable.

Red Flags

Metric tied to high-stakes rewards or punishments
Metric "improves" without obvious improvement in the underlying goal
People being measured can already articulate ways to game it
Single metric is the primary evaluation tool, no audit or paired-constraint

Verification

[ ] Goal underlying the metric specifically named
[ ] Proxy gap explicitly described; ≥3 gaming vectors listed
[ ] Goodhart mechanism category identified
[ ] Countermeasure design (multi-metric, audit, rotation) in place
[ ] Independent goal measurement scheduled with owner and retirement date

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