Abstract: In a Gaussian causal model, there may exist several criteria for the identification of the same causal effect, but the corresponding estimators may be different from each other. This paper consideres three popular identifiability criteria, front-door, back-door and instrumental variables criteria for causal effects, compares their estimate efficiencies and gives some simulations.
These results can offer guidances for choosing better identifiability criterion in practice.

Key words: Gaussian causal models, Causal effects, Front-door criterion, Back-door criterion, Instrumental variables