a mash data object, eg as created by mash_set_data
z_thresh
the z score threshold below which to call an effect null
est_cor
whether to estimate correlation matrix (TRUE) or the
covariance matrix (FALSE).
Details
Returns a simple estimate of the correlation matrix (or
covariance matrix) among conditions under the null. Specifically,
the simple estimate is the empirical correlation (or covariance)
matrix of the z scores for those effects that have (absolute) z
score < z_thresh in all conditions.