Post hoc analysis is an important procedure without which multivariate hypothesis testing would greatly suffer, rendering the chances of discovering false positives unacceptably high.

Post-hoc data analysis: benefits and limitations Curran-Everett, Douglas ; Milgrom, Henry Current Opinion in Allergy and Clinical Immunology: June 2013 - Volume 13 - Issue 3 - p 223–224

A review of the literature on clinical trials and post-hoc analysis makes it clear that clinicians, investors, and regulators should all view post-hoc analysis …