  The $\Delta H(M, \Delta M)$ method and its ability to determine intrinsic
switching field distributions of perpendicular recording media are numerically
studied. It is found that the presence of dipolar interactions in the range of
typical recording media substantially enhances the reliability of the $\Delta
H(M,\Delta M)$ method. In addition, a strong correlation is observed between
the precision of this method and a self-consistency-check of the data sets,
which is based upon a simple redundancy measure. This suggests that the latter
can be utilized as an efficient criterion to decide if a complete data analysis
is warranted or not.
