Wald estimator
= Wald estimator
{c}
{title2=$\widehat\beta_{\rm Wald}$}
{wiki}
For a binary <instrumental variable> $Z$, exposure $X$, and outcome $Y$, the Wald estimator is the ratio of the instrument's effect on the outcome to its effect on the exposure:
$$
\widehat\beta_{\rm Wald}
=\frac{\overline Y_{Z=1}-\overline Y_{Z=0}}
{\overline X_{Z=1}-\overline X_{Z=0}}.
$$
Under instrumental-variable assumptions it estimates a causal effect.