set of control variables , and unmeasured confounder for the relationship. Shi et al. presented formal conditions for a negative control outcome ,

# Stable Unit Treatment Value Assumption (SUTVA): For both and with regard to .
# Latent Exchangeability: Given and , the potential outcome is independent of the treatment.
# Irrelevancy: Ensures the irrelevancy of the treatment on the NCO.
## : There is no causal effect of on given