This code system http://hl7.org/fhir/evidence-classifier-code defines the following codes:

CodeDisplayDefinition
COVID19Specific COVID-19 specific articleAbout COVID-19.
COVID19Relevant COVID-19 relevant (but not specific) articleNot about COVID-19 but relevant to COVID-19 management or understanding.
COVID19HumanResearch COVID-19 human data in population, exposure, or outcomecontains human COVID-19 disease in the research data as any variable (population, exposure or outcome).
OriginalResearch Article includes original researchsuch as randomized trial, observational study.
ResearchSynthesis Article includes synthesis of researchsuch as systematic review, meta-analysis, rapid review.
Guideline Article includes guidelinefor clinical practice guidelines.
ResearchProtocol Article provides protocol without resultsfor research protocols.
NotResearchNotGuideline Article is neither research nor guidelinefor things that are not research reports, research protocols or guidelines.
Treatment Article about treatmentabout therapeutic interventions.
PreventionAndControl Article about prevention and controlabout preventive care and interventions.
Diagnosis Article about diagnosisabout methods to distinguish having or not having a condition.
PrognosisPrediction Article about prognosis or predictionabout predicting risk for something or risk factors for it.
RatedAsYes Rated as yes, affirmative, positive, present, or include
RatedAsNo Rated as no, negative, absent, or excludeRated as no, negative, absent, or exclude.
NotAssessed Not rated, not assessedNeither rated as yes nor rated as no.
RatedAsRCT classified as randomized controlled trialclassified as randomized controlled trial.
RatedAsControlledTrial classified as nonrandomized controlled trial (experimental)classified as nonrandomized controlled trial (experimental).
RatedAsComparativeCohort classified as comparative cohort study (observational)classified as comparative cohort study (observational).
RatedAsCaseControl classified as case-control studyclassified as case-control study.
RatedAsUncontrolledSeries classified as uncontrolled cohort (case series)classified as uncontrolled cohort (case series).
RatedAsMixedMethods classified as mixed-methods studyclassified as mixed-methods study.
RatedAsOther classified as other concept (not elsewhere classified)classified as other concept (not elsewhere classified).
RiskOfBias Risk of bias assessmentRisk of bias assessment.
NoBlinding No blindingNo blinding.
AllocConcealNotStated Allocation concealment not statedAllocation concealment not stated.
EarlyTrialTermination Early trial terminationEarly trial termination.
NoITT No intention-to-treat analysisNo intention-to-treat analysis.
Preprint Preprint (not final publication)Results presented in preprint (pre-final publication) form.
PreliminaryAnalysis Preliminary analysisPreliminary analysis.
BaselineImbalance Baseline imbalancesDifferences between groups at start of trial may confound or bias the findings.
SubgroupAnalysis Subgroup analysisSubgroup analysis.
<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="Commonly used classifiers for evidence sets."/><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/evidence-classifier-code"/><content value="complete"/><concept><code value="COVID19Specific"/><display value="COVID-19 specific article"/><definition value="About COVID-19."/></concept><concept><code value="COVID19Relevant"/><display value="COVID-19 relevant (but not specific) article"/><definition value="Not about COVID-19 but relevant to COVID-19 management or understanding."/></concept><concept><code value="COVID19HumanResearch"/><display value="COVID-19 human data in population, exposure, or outcome"/><definition value="contains human COVID-19 disease in the research data as any variable (population, exposure or outcome)."/></concept><concept><code value="OriginalResearch"/><display value="Article includes original research"/><definition value="such as randomized trial, observational study."/></concept><concept><code value="ResearchSynthesis"/><display value="Article includes synthesis of research"/><definition value="such as systematic review, meta-analysis, rapid review."/></concept><concept><code value="Guideline"/><display value="Article includes guideline"/><definition value="for clinical practice guidelines."/></concept><concept><code value="ResearchProtocol"/><display value="Article provides protocol without results"/><definition value="for research protocols."/></concept><concept><code value="NotResearchNotGuideline"/><display value="Article is neither research nor guideline"/><definition value="for things that are not research reports, research protocols or guidelines."/></concept><concept><code value="Treatment"/><display value="Article about treatment"/><definition value="about therapeutic interventions."/></concept><concept><code value="PreventionAndControl"/><display value="Article about prevention and control"/><definition value="about preventive care and interventions."/></concept><concept><code value="Diagnosis"/><display value="Article about diagnosis"/><definition value="about methods to distinguish having or not having a condition."/></concept><concept><code value="PrognosisPrediction"/><display value="Article about prognosis or prediction"/><definition value="about predicting risk for something or risk factors for it."/></concept><concept><code value="RatedAsYes"/><display value="Rated as yes, affirmative, positive, present, or include"/></concept><concept><code value="RatedAsNo"/><display value="Rated as no, negative, absent, or exclude"/><definition value="Rated as no, negative, absent, or exclude."/></concept><concept><code value="NotAssessed"/><display value="Not rated, not assessed"/><definition value="Neither rated as yes nor rated as no."/></concept><concept><code value="RatedAsRCT"/><display value="classified as randomized controlled trial"/><definition value="classified as randomized controlled trial."/></concept><concept><code value="RatedAsControlledTrial"/><display value="classified as nonrandomized controlled trial (experimental)"/><definition value="classified as nonrandomized controlled trial (experimental)."/></concept><concept><code value="RatedAsComparativeCohort"/><display value="classified as comparative cohort study (observational)"/><definition value="classified as comparative cohort study (observational)."/></concept><concept><code value="RatedAsCaseControl"/><display value="classified as case-control study"/><definition value="classified as case-control study."/></concept><concept><code value="RatedAsUncontrolledSeries"/><display value="classified as uncontrolled cohort (case series)"/><definition value="classified as uncontrolled cohort (case series)."/></concept><concept><code value="RatedAsMixedMethods"/><display value="classified as mixed-methods study"/><definition value="classified as mixed-methods study."/></concept><concept><code value="RatedAsOther"/><display value="classified as other concept (not elsewhere classified)"/><definition value="classified as other concept (not elsewhere classified)."/></concept><concept><code value="RiskOfBias"/><display value="Risk of bias assessment"/><definition value="Risk of bias assessment."/></concept><concept><code value="NoBlinding"/><display value="No blinding"/><definition value="No blinding."/></concept><concept><code value="AllocConcealNotStated"/><display value="Allocation concealment not stated"/><definition value="Allocation concealment not stated."/></concept><concept><code value="EarlyTrialTermination"/><display value="Early trial termination"/><definition value="Early trial termination."/></concept><concept><code value="NoITT"/><display value="No intention-to-treat analysis"/><definition value="No intention-to-treat analysis."/></concept><concept><code value="Preprint"/><display value="Preprint (not final publication)"/><definition value="Results presented in preprint (pre-final publication) form."/></concept><concept><code value="PreliminaryAnalysis"/><display value="Preliminary analysis"/><definition value="Preliminary analysis."/></concept><concept><code value="BaselineImbalance"/><display value="Baseline imbalances"/><definition value="Differences between groups at start of trial may confound or bias the findings."/></concept><concept><code value="SubgroupAnalysis"/><display value="Subgroup analysis"/><definition value="Subgroup analysis."/></concept></CodeSystem>