*Geek Box: Post-Hoc Secondary Analysis

*Geek Box: Post-Hoc Secondary Analysis

The literal translation of the Latin term ‘post hoc’ is ‘after this’, i.e., something which occurs after an event. In research, a post hoc analysis is an analysis which is undertaken after a trial has concluded, using data from that trial, to look at a question that was not pre-specified.

The key feature of a post-hoc analysis is that it is secondary to the main study, and the question it is addressing is not a primary research question. Because a post hoc analysis is a secondary analysis and not part of the pre-planned and pre-registered study, a post-hoc analysis is, in effect, an observational study. It can look at relationships, but not causality.

Post-hoc analyses are very useful, and informative, tools in research, particularly where a well-conducted controlled trial generates a voluminous data set. Like all research designs, it is important to understand their place, and what they can show [associations] and cannot show [cause-effect].