Measurement Rationale Extension

Canonical	../StructureDefinition/measurement-rationale
Status	draft · 1.26.0
Base	Extension (constraint)
Context	ObservationDefinition (element)
Source	FSH · JSON

Why this measurement definition exists: the specific ambiguity or unit trap it prevents. Required on every definition, because a definition that cannot name the failure it prevents is a guess, and the failures this guards against (affine unit conversions, off-by-one ordinal scales) produce numbers that render and validate while being wrong. Carried as an extension because R4's ObservationDefinition has no narrative element; it retires into description on a move to R5.

Invariants

Every rule in force on a conforming instance. This profile rows are stated here; inherited rows come from the base resource and are listed so that a constraint named on an element is findable. Invariant keys elsewhere on this page link into this table.

Key	Source	Severity	On	Rule
ele-1	inherited	error	Extension	All FHIR elements must have a @value or children hasValue() or (children().count() > id.count())
ext-1	inherited	error	Extension	Must have either extensions or value[x], not both extension.exists() != value.exists()