# Granger Causality coefficient comparison

I am working with a time series data and found that $a_t$ Granger causes $b_{t+1}$ and $b_t$ granger causes $a_{t+1}$. The results were obtained through Stata.

1. With the coefficients obtained, is it possible to determine which Granger causal direction is stronger? If it can't be determined by just looking at the coefficients, is there a method to do so?

Also, Granger causality was tested on 2 conditions. In one subset, a policy was adopted. In the other subset, the policy was not adopted. The results was that a granger causes $b_{t+1}$ in both cases.

2. Is there a way to test whether the Granger causality coefficient in condition one was significantly different in condition two? One idea is to introduce an interaction term, but is this possible with Granger causality tests?