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A Questionnaire defined with the eHealth profile ehealth-questionnaire-advanced (see https://docs.ehealth.sundhed.dk/latest-released/ig/StructureDefinition-ehealth-questionnaire-advanced.html) can contain zero, one or more expressions performing a calculation based on answers to questions in the Questionnaire. The expression can make use of zero, one or more variables which identify the particular question/answers more concisely.

Defining a Variable

A variable intended for use in an expression (see below) is defined using the extension variable. An example of a variable is shown below as an excerpt of a Questionnaire (in profile ehealth-questionnaire-advanced) in JSON:

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The variable here is defined at Questionnaire root level referencing a particular question through its Questionnaire.item.linkId. On evaluation in a QuestionnaireResponse, the variable will hold the integer value of the answer (presumably, the referenced Questionnaire.item has integer answer type).

An example of a variable evaluating to an ordinal value is shown below as an excerpt of a Questionnaire (in profile ehealth-questionnaire-advanced) in JSON:

 {
  "url": "http://hl7.org/fhir/StructureDefinition/variable",
  "valueExpression": {
    "name": "BreathingDifficulty",
    "language": "text/fhirpath",
    "expression": "iif(QuestionnaireResponse.repeat(item).where(linkId='1.2.208.176.1.5.1,6e6bb131-debd-4675-803b-7d783a75acc6,Sundhedsdatastyrelsen').answer.valueString = 'Severe', 2,
                   iif(QuestionnaireResponse.repeat(item).where(linkId='1.2.208.176.1.5.1,6e6bb131-debd-4675-803b-7d783a75acc6,Sundhedsdatastyrelsen').answer.valueString = 'Normal', 1, {}))"
  }
}

The expression above relies on the definer to ensure consistency between the actual answer values (in Questionnaire.item.answerOption.answer[x]) and ordinal values possibly assigned in Questionnaire.item.answerOption.ordinalValue.

Defining a Calculation Expression

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• language - the expression language. The supported language is a subset of FHIRPath described below. The expression language is specified as "text/fhirpath".

• expression - the expression

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Expression Language

The supported expression language is the following subset of FHIRPath:

• Arithmetic: multiplication, division, addition & subtraction only

• Parentheses ‘(' and ')'

• Constants

• The equals operation (=) for primitive types

• The iif function

Releasing a Questionnaire

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