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mcnamara_fallacy
The McNamara Fallacy occurs when decision-making relies exclusively on quantitative metrics while ignoring qualitative factors that are harder to measure but equally or more important. Named after Robert McNamara, who used body counts as the primary measure of success in the Vietnam War, this fallacy proceeds in steps: first measuring what is easily measurable, then disregarding what cannot be measured, and finally assuming that what cannot be measured is not important.
A hospital evaluates doctors solely by the number of patients seen per hour. Dr. A sees 8 patients per hour with quick consultations. Dr. B sees 4 but spends time on thorough diagnosis and patient education. Management promotes Dr. A, ignoring that Dr. B has better patient outcomes and fewer readmissions.
A school district evaluates teacher performance exclusively through students' standardized test scores. Teachers begin 'teaching to the test,' cutting art, physical education, and class discussions. Test scores rise slightly, but student curiosity, mental health, and long-term love of learning quietly deteriorate — none of which appear in the metrics.
A social media platform measures content quality purely by engagement metrics: likes, shares, and watch time. Content optimized for outrage and shock performs best by these measures, and the algorithm promotes it heavily — while nuanced, accurate, and constructive content, which is harder to quantify, steadily disappears from feeds.
Binary (yes/no) questions an LLM must answer to identify this aspect:
Is a decision being made based primarily on quantitative metrics?
Type: binaryAre important qualitative, subjective, or hard-to-measure factors being ignored?
Type: binaryDoes the metric actually capture what matters for the decision?
Type: binaryThe McNamara Fallacy occurs when decision-making relies exclusively on quantitative metrics while ignoring qualitative factors that are harder to measure but equally or more important. Named after Robert McNamara, who used body counts as the primary measure of success in the Vietnam War, this fallacy proceeds in steps: first measuring what is easily measurable, then disregarding what cannot be measured, and finally assuming that what cannot be measured is not important.
Numbers feel objective, precise, and comparable. Qualitative factors are ambiguous and harder to defend in meetings or reports, so they get sidelined even when everyone knows they matter.
Explicitly list and discuss important qualitative factors alongside quantitative metrics. Use balanced scorecards and ask what important aspects are NOT captured by the current measurements.
This fallacy dominates corporate KPI culture, educational testing (teaching to the test), and policing (crime statistics vs. community trust). Goodhart's Law is a closely related phenomenon.
Use these tools to detect, analyze, or train this aspect.