Direct answer

Measurement begins with a decision and a valid comparison. Preserve context, expose formulas and distinguish observation from causal evidence.

Practical steps

  1. Write the question and decision.
  2. Choose primary and guardrail metrics.
  3. Record baseline and changes.
  4. Compare like periods and segments.
  5. Publish findings and limitations.

Common mistakes

  • Single-metric success.
  • Universal CTR assumptions.
  • Calling correlation causation.

Limitations

  • Attribution is incomplete.
  • Small samples create unstable estimates.

Primary sources