Negative Control Outcome (NCO)
Definition
An NCO is an outcome variable guaranteed a priori to be unaffected by the treatment’s causal influence, yet still cast in the shadow of the same confounder . By contrast, an NCE (negative control exposure) is an exposure with no causal effect on the outcome. If the “apparent effect” on an NCO is nonzero → a signal of unmeasured confounding (detection) → correct for it via proximal methods.
Intuitive Understanding
The canary in the coal mine — if something that should not move does move, it means confounding control has failed. Given enough NCOs, their pervasiveness lets you reconstruct in reverse.
Related Concepts
- Proximal Causal Inference — NCO/NCE bridge identification
- Partial Identification · Sensitivity Analysis
Key Papers
- Lipsitch, Tchetgen Tchetgen & Cohen, “Negative controls”, Epidemiology 21(3), 2010
- Shi, Miao & Tchetgen Tchetgen, negative controls / proximal review, 2020
- Related prior work: Zhou et al. 2024 Biometrika; Zheng–Franks 2023 JASA