In section 3.4 we showed that the two-level model
can be inferred upon using the summary statistics of the
first-level model inference (equation 14).
This means that all-in-one and split-level inference is equivalent
when we infer on the top-level regression parameters. Here we use
four different null artificial datasets from the two-level model
for 
voxels to validate the fast approximation and MCMC/BIDET
inference we perform on equation 14.