Let’s state the problem as one of associating some sort of absence, presence, or in-between indicator with some X in a patient, or some other subject…
There is some discussion about this topic in SPECPR-118, in which Ian McNicoll made the comment:
I think we need to do a bit more thinking about the pros and cons and the somewhat different requirements of e.g negating a diagnosis vs. negating a symptom.
This is exactly right - there are different kinds of Xs. There are observable Xs, including things we use instruments to observe (which we generally assume to be reliable in a practical sense). So presence/absence claims can reasonably be made in cases where the X being observed (e.g. pregnancy, MRSA, being a smoker) is the same thing the claim is made about (is pregnant, neg MRSA, non-smoker). In this case, the presence / absence can reasonably be said to be part of the reported reality of the X in question.
However, if the claim is about a C (some ‘condition’) where C cannot be directly observed (or is not, in the current situation) then we are looking at an epistemic claim about knowledge of C, based on observed X, what X means in the context of patient type P, and so on. There is a range of epistemic claims that could be made about Cs, e.g. the following:
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doesn’t exist - 100% sure C not present in patient - e.g. diabetes type I, based on negative oral glucose test
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may exist - C is effectively one branch of a differential diagnosis or other assessment
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does exist - 100% sure C present in patient - e.g. diabetes type I, based on +ve oral glucose test
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no risk of C in future - 100% sure C will not occur, e.g. BRCA1 or 2 breast cancer, based on genetic test (we assume the latter is bullet-proof)
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risk of C in future - some likelihood of C occurring
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guarantee of C occurring in future - future reaction to exposure to bee venom in a patient known to be hyper-allergic to been venom
This basically boils down to:
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it may be reasonable to allow presence or absence of true ‘observables’ to be encoded in a binary way (what we think of as Observations in openEHR)
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claims regarding any kind of assessment, opinion, diagnosis, etc of something we don’t directly observe as such are epistemic claims, i.e. claims about type of knowledge we have of some C, and are not encodable as a Boolean ‘existence’ idea, but only as a level of certainty or similar. (what we think of as Evaluations in openEHR)
To make things somewhat annoying, there is probably a grey area between the two. For example, ‘pregnant’ could arguably be regarded as a direct observation or an assessment. But I think for 95% of cases things are obvious.
So my conclusion is that the way to record presence / absence of true observables could reasonably be done in a simple way, while any type of assessment has to be recorded in a way that a) allows some range of certainty, b) can include the temporal aspect (now, future etc) and c) can reflect the current state of the investigative process.
Another annoyance that may prevent simple modelling is that EHRs often include statements like ‘is diabetic’, e.g. reported by an obviously diabetic patient about her diagnosis from 20y ago. Such statements are not in themselves assessments, they are reports of the outcome of an earlier process. As such, it may be reasonable to report such things in a more or less binary way, e.g. is / is not diabetic.
I’m not a fan of negation or any other variety of presence, absence, risk of etc being part of terminology, at least not pre-coordinated with the ontological part (doing so is a total confusion about what the terminology expresses). A typology of negation / epistemic claims could potentially exist in some separate part of a terminology e.g. SNOMED, to be used to code information model property like ‘epistemic_status’, or similar.
Aside: apparently the FHIR approach to representing things like ‘no known allergies’ is to infer it by seeing if an allergies list is empty or not. That sounds like a bad idea to me. If ‘no known allergies’ is understood as a clinically meaningful statement made by e.g. a GP (based on reliable knowledge about the patient), checking for a list being empty in some EMR system isn’t at all the same thing. All that latter does is establish that no allergies have been recorded on this particular system.
