Concepts / Measurement
The McNamara fallacy.
What is easy to measure can crowd out what matters. The fallacy is to rely on what can be counted, set aside what cannot, and in the end take the numbers for the whole picture.
The term was coined by the social scientist Daniel Yankelovich in the early 1970s. It refers to Robert McNamara, US Secretary of Defense during the Vietnam War, whose assessment of progress leaned heavily on quantitative indicators such as body counts.
How it unfolds
Four steps, as Yankelovich described them.
Each step seems reasonable on its own. Taken together, they turn a partial picture into a confident one.
- 01
Measure what is easy
Count what is simple to count and report.
- 02
Set aside what is hard
Give little attention to what resists counting, such as trust, behaviour or the quality of a service.
- 03
Treat it as unimportant
Assume that what is not measured does not need attention.
- 04
Assume it is not there
Conclude that what cannot be measured easily does not really exist.
Where it can show up
When activity stands in for results.
These are general patterns in political and organisational analysis, not findings about any particular party, campaign or programme.
Rallies and persuasion
Counting rallies and crowds, rather than assessing whether minds have changed.
Enrolments and service
Reporting how many people were enrolled, rather than whether the service reached them well.
Activity and concerns
Tracking meetings and events, rather than understanding what people are worried about.
Outputs and outcomes
Measuring what was delivered, rather than what changed as a result.
A close relative
Not the same as Goodhart's law.
Goodhart's law is about a measure that is distorted once it becomes a target. The McNamara fallacy is about everything that is never measured at all. One bends the numbers; the other narrows what the numbers can see. Both can operate at once.
How to guard against it
Count what you can. See what you cannot.
Numbers remain essential. The aim is to keep them from becoming the only evidence that counts.
- Start from what matters, then ask how it could be observed, not the other way round.
- Use qualitative evidence alongside numbers: field visits, interviews and open-ended feedback.
- Report what cannot be measured, and say so plainly, instead of leaving it out.
- Treat missing data as missing knowledge, not as evidence that there is no problem.
- Let those closest to the ground challenge the dashboard.
Origins and further reading
Where the idea comes from.
Yankelovich introduced the term in his writing on business and marketing in the early 1970s; sources differ on its first appearance. It has since been applied in public policy, medicine and management.
- Yankelovich, D. (1972). Corporate Priorities: A Continuing Study of the New Demands on Business. Daniel Yankelovich, Inc.
- O'Mahony, S. (2017). Medicine and the McNamara fallacy. Journal of the Royal College of Physicians of Edinburgh, 47(3), 281–287.
- Muller, J. Z. (2018). The Tyranny of Metrics. Princeton University Press.
About this concept
A general idea, not a verdict.
This page explains a general concept from social science and management. It does not describe or assess any particular party, government, programme or election. Related: Goodhart's law and the perspective When the ground stops reaching the top.