Hi Colin,
This is a tricky space indeed. There is no absolutely right answer. In reality, we are all bumbling along as best we can in the circumstances, and trying to model these concepts faithful to the original, often well-validated, scores & scales, but most of all ensuring that each archetype is as clinically safe for implementation as possible. All contributions are welcome, especially ideas that come from a slightly different direction to provide checks and balances to our assumptions.
The notion of a generic representation of severity scale (outside of the formal Score/Scale territory) is tricky. My advice when modelling severity and using a SNOMED as a drop-down list (not an ordinal for reasons that you outline quite rightly) is to keep it to 3 values - mild/moderate/severe. Back in the day, I saw lists that included trivial/mild/mild-to-moderate/moderate/moderate-to-severe/severe/very severe/fatal. Yes, a fatal symptom! And with a list like that, it is absolutely not possible to get any inter-rater consistency because everyone’s definitions of/criteria for each term will be different. My severe could well be someone else’s mild-to-moderate. So with the KISS principle in mind, we usually strip down this kind of subjective severity assessment towards the 3 values, hoping that clinicians can reasonably differentiate between them - unless there is good reason and explicit definitions to justify otherwise.
In the past, we have dabbled in interpolation for some models but it felt quite unsafe, and now avoid it as a CKM modelling approach nowadays, again for the reasons that you outline.
You may well be right that the authors are designing scores without a correct understanding of how they should be used in statistics. I’m certainly no expert on that and you’ve clearly explored this area more than I. However, it is a CKM Editor responsibility to represent the Score/Scale faithfully, according to copyright etc. If an existing, validated, frequently used score or scale represents values with a score, which are often used as part of a calculation for a total score or for graphing trends etc, it will often be modelled as a DV_ORDINAL BUT if it is not clinically safe to use (which is why clinical informaticians should be modelling archetypes) then I’d advise a different data type be used, usually DV_CODED_TEXT to supply the list of options alone. Ordering a value set, without numeric ranking - hmmm, not sure we’ve seen a use case yet.
So we do try to model ordinals where ordinals are appropriate - otherwise, we run the risk of inappropriate implementation. Is there a use case/archetype you think we have modelled incorrectly or inappropriately?
This thread is a natural follow on to content but not aligned with the topic. Perhaps we should look at creating another thread for the purpose if this conversation continues.
I don’t see incompatibility with the other threads that you mention, but curious to understand more of what you are thinking. Perhaps we should continue discussions in each of those respective threads if you are seeking further clarity?
Cheers
Heather