And yet in both these cases we at least _try_ to come up with quantifiable results of our observations. The point is that without them we are not really capable of coming up with any meaningful conclusions.
> Very occasionally there are great scientific studies of software
For me it seems the body of software available to analyse empirically is large enough now to start doing it and it is happening. What's important is that none of the empirical studies I know measure anything named "technical debt".
>> Talking about "technical debt" of software system is no more useful than talking about its scent.
> Why do you think talking about its scent is not useful?
Because it does not provide any meaningful insight into what should or should not be done to improve it.