Bioequivalence and Bioavailability Forum

I would like to re-open this thread, in light of the final version of EMA's guidance on Transdermal Patches (link here). This document guide us to the "Guideline on the Pharmacokinetic and clinical evaluation of modified-release dosage forms" to describe with details how to conduct Skin Irritation and Sensitization study and Adhesion study(annex I and annex II)
Let us talk about the Adhesion bit. EMA states: "The adhesion should be measured as the percentage of area that remains adhered at the end of the dosing interval." (my emphasis)
By that I assume that the variable of adhesion will be continuous. So I ask: how would one measure that with precision? In the draft of this guidance they suggested to categorize and treat as scores (similar to FDA's draft guidance) but with a statistical analysis that didn't make sense (now it makes more sense).
I've seen this method but I'm not sure if it is applicable, since it was suggested to use for scores (categorical data) and not for continuous. The precision in that method of assessment of adhesion would enough to treat the variable as continuous?
Anyone know a better method of assessment?