Error Asymmetry
When being wrong in one direction costs far more than being wrong in the other, which makes a single accuracy figure close to meaningless.
Reviewed July 17, 2026Stable
When not to use it
- Where the costs genuinely are symmetric, which is rare and worth verifying rather than assuming in either direction.
- As a reason to ignore accuracy entirely; it remains necessary and is not sufficient.
- Where the operating point has already been set from a stated cost analysis, which is the practice this concept exists to encourage.
Reach for something else instead
- Capped constraint — fix a maximum on the costly error rate and minimise the other subject to it, avoiding the need to convert costs into a common unit.
- Subgroup reporting — publish error rates by population, which reveals concentration that an aggregate conceals.
Further reading
- Kleinberg et al. (2016), Inherent Trade-Offs in the Fair Determination of Risk Scores — why error rates cannot be equalised across groups while calibration holds.
- Wong et al. (2021), External Validation of a Widely Implemented Proprietary Sepsis Prediction Model — alert burden against omission, where only one side leaves a record.
Primary sources, listed so you can check the claims on this page rather than take them on trust.
Where people go wrong
- Comparing systems on a single balanced metric when their deployments have different cost structures.
- Reporting aggregate error rates where the errors concentrate on an identifiable subgroup.
- Assuming an unmeasured error is a rare one, when it may simply leave no artefact.
At a glance
FieldFoundations
Core pointone accuracy figure hides a cost weighting
Three questionsreversible, borne by whom, visible
Formal remedycost matrix or capped constraint
Common trapthe costlier error is the less measurable one
DifficultyBeginner → Intermediate
Where this sits
A starting point. Nothing needs to come before it.
0Levelstarting point
0Needs firstnothing
0Opens upnothing further
1Areastays here
Computed from the prerequisite graph, not assigned. How this works