openEHR-technical Digest, Vol 64, Issue 6

Thomas Beale thomas.beale at
Thu Jul 6 09:24:02 EDT 2017

Hi Gerard,

On 07/06/2017 07:46, GF wrote:
> Dear Silje,
> Questions in questionnaire are observations.
> But what is it, when a Scale makes use of existing data in the 
> database and calculates an aggregate result?
> (E.g. BMI)
> Isn’t the latter an evaluation of existing observations by means of a 
> rule?

Just on this question - a BMI might be computed, but it's still just a 
datum relating to an 'individual', as ontologists would say, so it's an 
OBSERVATION in openEHR terms. An EVALUATION is a opinion generated by 
comparing fact(s) about an individual to a knowledge based in order to 
classify the individual in some way, e.g. 'overweight'.

> In the case of BMI the weight and length are real observable 
> properties of a (human) body.
> Question: Is the BMI an observable property? I think not. It is an 
> aggregate, an evaluation.

not observable in the literal sense, but the view we take in openEHR is 
that an Observation is the apprehension of data relating to the 
individual, by means of examination and / or instruments. A BMI clearly 
falls under this category of information.

It can be the basis for an Evaluation if compared to some BMI normal 
ranges, to generate an Evaluation such as 'overweight', as above - this 
is an inference. A machine might do this.

Someone will probably bring up scores like Apgar, and say they are some 
sort of inference, since the constituent scores are based on 
statistical/clinical pictures of what is healthy or not (e.g. HR >= 100 
bpm etc). Philosophically speaking, this is true, and in theory they 
should be an EVALUATION. For practical reasons they are generally 
modelled as OBSERVATIONs, since they tend to act as a means of reporting 
physical examinations (in a quantitative way), and they get used as 
triage variables for determining which treatment path to follow.

In a more perfect world, scores might have their own ENTRY type, but I 
don't think the lack of it has done any harm to date.

- thomas

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