  The Y-test is a useful tool for detecting missing confounders in the context
of a multivariate regression.However, it is rarely used in practice since it
requires identifying multiple conditionally independent instruments, which is
often impossible. We propose a heuristic test which relaxes the independence
requirement. We then show how to apply this heuristic test on a price-demand
and a firm loan-productivity problem. We conclude that the test is informative
when the variables are linearly related with Gaussian additive noise, but it
can be misleading in other contexts. Still, we believe that the test can be a
useful concept for falsifying a proposed control set.
