There are so many Latin terms in medicine. And if you don’t have a medical degree, which usually comes with a couple of semesters studying Latin, you might find it hard to remember them all. In clinical trials, the terms ad hoc and post hoc are used to refer to data analyses. In this blog, we look at the definitions and differentiate these concepts.
Ad hoc
Ad hoc / ad-hoc translates from Latin as “for this” and refers to when necessary or needed – to answer a specific question – and can occur both during and after a clinical trial.
We recommend an ad hoc subgroup analysis of the ORATORIO trial to identify the targeted population that has the maximal benefit of the promising drug, ocrelizumab, with the least exposure to uncertain side effects.
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Post hoc
And post hoc / post-hoc translates as “after this” and refers to unplanned, usually retrospective analysis.
In the instances where treatment effects may have been underestimated, valuable information may be lost if buried within a composite endpoint. In all these cases, post hoc analyses of data become relevant in informing practitioners about clinical benefits or safety signals that may not be captured by the primary endpoint.
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On an ad-hoc basis
The expression on an ad-hoc basis is an idiom that means “unplanned,” “as a response to a specific situation.” Here is an example:
If implemented, this function is often used as a means to dispense drug on an ad-hoc basis (e.g. if a subject is going on vacation and will need more drug than usual).
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Here, on an ad-hoc basis means “single-time unplanned use.”
Other expressions
You may also come across expressions post ad hoc analysis and (rarely) pre ad hoc analysis.
This is a post ad hoc analysis, so it is not convincible that no additional statistical analysis could be added because of a previously approved statistical analysis plan which is not submitted with this manuscript at all.
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Pre-and post ad hoc analysis revealed a significant difference between the starting BMI and the BMI following 41 days of LG839 intake in the 21 individuals.
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Basically, pre ad hoc = ad hoc and post ad hoc = post hoc. If you are writing a text, my advice would be to avoid these constructs and use simple ad hoc and post hoc.
Which other Latin terms would you like me to explore?
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