This code system http://hl7.org/fhir/certainty-type defines the following codes:

CodeDisplayDefinition
Overall Overall certaintyOverall certainty of evidence (quality of evidence).
RiskOfBias Risk of biasmethodologic concerns reducing internal validity.
Inconsistency Inconsistencyconcerns that findings are not similar enough to support certainty.
Indirectness Indirectnessconcerns reducing external validity.
Imprecision Imprecisionfuzzy or wide variability.
PublicationBias Publication biaslikelihood that what is published misrepresents what is available to publish.
DoseResponseGradient Dose response gradienthigher certainty due to dose response relationship.
PlausibleConfounding Plausible confoundinghigher certainty due to risk of bias in opposite direction.
LargeEffect Large effecthigher certainty due to large effect size.
<status value="active"/><experimental value="false"/><date value="2020-12-28T16:55:11+11:00"/><publisher value="HL7 (FHIR Project)"/><contact><telecom><system value="url"/><value value="http://hl7.org/fhir"/></telecom><telecom><system value="email"/><value value="fhir@lists.hl7.org"/></telecom></contact><description value="The aspect of quality, confidence, or certainty."/><jurisdiction><coding><system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/><code value="001"/><display value="World"/></coding></jurisdiction><caseSensitive value="true"/><valueSet value="http://hl7.org/fhir/ValueSet/certainty-type"/><content value="complete"/><concept><code value="Overall"/><display value="Overall certainty"/><definition value="Overall certainty of evidence (quality of evidence)."/></concept><concept><code value="RiskOfBias"/><display value="Risk of bias"/><definition value="methodologic concerns reducing internal validity."/></concept><concept><code value="Inconsistency"/><display value="Inconsistency"/><definition value="concerns that findings are not similar enough to support certainty."/></concept><concept><code value="Indirectness"/><display value="Indirectness"/><definition value="concerns reducing external validity."/></concept><concept><code value="Imprecision"/><display value="Imprecision"/><definition value="fuzzy or wide variability."/></concept><concept><code value="PublicationBias"/><display value="Publication bias"/><definition value="likelihood that what is published misrepresents what is available to publish."/></concept><concept><code value="DoseResponseGradient"/><display value="Dose response gradient"/><definition value="higher certainty due to dose response relationship."/></concept><concept><code value="PlausibleConfounding"/><display value="Plausible confounding"/><definition value="higher certainty due to risk of bias in opposite direction."/></concept><concept><code value="LargeEffect"/><display value="Large effect"/><definition value="higher certainty due to large effect size."/></concept></CodeSystem>