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

Code Display Definition
COVID19Specific COVID-19 specific article About COVID-19.
COVID19Relevant COVID-19 relevant (but not specific) article Not about COVID-19 but relevant to COVID-19 management or understanding.
COVID19HumanResearch COVID-19 human data in population, exposure, or outcome contains human COVID-19 disease in the research data as any variable (population, exposure or outcome).
OriginalResearch Article includes original research such as randomized trial, observational study.
ResearchSynthesis Article includes synthesis of research such as systematic review, meta-analysis, rapid review.
Guideline Article includes guideline for clinical practice guidelines.
ResearchProtocol Article provides protocol without results for research protocols.
NotResearchNotGuideline Article is neither research nor guideline for things that are not research reports, research protocols or guidelines.
Treatment Article about treatment about therapeutic interventions.
PreventionAndControl Article about prevention and control about preventive care and interventions.
Diagnosis Article about diagnosis about methods to distinguish having or not having a condition.
PrognosisPrediction Article about prognosis or prediction about 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 exclude Rated as no, negative, absent, or exclude.
NotAssessed Not rated, not assessed Neither rated as yes nor rated as no.
RatedAsRCT classified as randomized controlled trial classified 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 study classified as case-control study.
RatedAsUncontrolledSeries classified as uncontrolled cohort (case series) classified as uncontrolled cohort (case series).
RatedAsMixedMethods classified as mixed-methods study classified as mixed-methods study.
RatedAsOther classified as other concept (not elsewhere classified) classified as other concept (not elsewhere classified).
RiskOfBias Risk of bias assessment Risk of bias assessment.
NoBlinding No blinding No blinding.
AllocConcealNotStated Allocation concealment not stated Allocation concealment not stated.
EarlyTrialTermination Early trial termination Early trial termination.
NoITT No intention-to-treat analysis No intention-to-treat analysis.
Preprint Preprint (not final publication) Results presented in preprint (pre-final publication) form.
PreliminaryAnalysis Preliminary analysis Preliminary analysis.
BaselineImbalance Baseline imbalances Differences between groups at start of trial may confound or bias the findings.
SubgroupAnalysis Subgroup analysis Subgroup 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>