Glossary of Systematic Literature Review (SLR) Terminology

This alphabetically ordered glossary provides definitions for terms and concepts encountered in systematic literature reviews (SLRs), meta-analyses, and other evidence synthesis methodologies.

A

• Abstract Screening: The process of reviewing study abstracts to determine if they meet inclusion criteria for a systematic review.
• A Priori: Decisions, criteria, or methods determined before beginning a systematic review, typically documented in the protocol.
• Aggregate Data: Combined numerical data from multiple studies, as opposed to individual participant data.
• Article Retrieval: The process of obtaining full-text articles of studies identified through database searches.
• Assessment of Methodological Quality: Evaluation of the design and execution of included studies to determine risk of bias or methodological rigor.

B

• Best Evidence Synthesis: A systematic approach that focuses on the highest quality evidence available to answer a research question.
• Between-Study Variance: In meta-analysis, the variation in true effect sizes across studies, typically denoted as τ² (tau-squared).
• Bibliographic Database: A searchable electronic collection of published literature (e.g., PubMed, EMBASE, Web of Science).
• Bibliometrics: Statistical analysis of publications, often used to map research trends or impact in a field.
• Boolean Operators: Terms (AND, OR, NOT) used to combine search terms in database searches.

C

• CADIMA: A web-based tool designed to support the conduct of systematic reviews in environmental and agricultural sciences.
• CASP Checklists: Critical Appraisal Skills Programme tools for assessing the quality of various study designs.
• Citation Chasing: The process of examining the reference lists of included studies to identify additional relevant studies (backward citation chasing) or finding studies that have cited the included studies (forward citation chasing).
• Citation Management Software: Tools (e.g., EndNote, Zotero, Mendeley) for organizing and managing references throughout the review process.
• Cochrane Collaboration: An international organization that produces and disseminates systematic reviews of healthcare interventions.
• Cochrane Handbook: A comprehensive guide for conducting systematic reviews of interventions, published by the Cochrane Collaboration.
• Cochrane Review: A systematic review conducted according to Cochrane Collaboration methodology.
• Confidence Interval (CI): A statistical measure indicating the range within which the true effect is likely to lie, with a specified level of confidence.
• CONSORT Statement: Consolidated Standards of Reporting Trials; guidelines for reporting randomized controlled trials.
• Critical Appraisal: Systematic evaluation of research quality, validity, and relevance.

D

• Data Abstraction/Extraction: The process of collecting relevant information from included studies using standardized forms.
• Data Extraction Form: A standardized tool used to consistently collect relevant information from included studies.
• Data Synthesis: The combining of findings from multiple studies, either quantitatively or qualitatively.
• Database Bias: Systematic error resulting from the selection of databases for searching.
• Deduplication: The process of identifying and removing duplicate study records retrieved from multiple database searches.
• Directed Acyclic Graph (DAG): A visual tool used to identify potential biases and confounders in research.
• Disaggregated Data: Individual data points rather than summary statistics, often referring to individual participant data.
• Dissemination Bias: Systematic differences between completed research studies and those made publicly available.
• DOSS Method: The Database, Online repositories, Supplementary files, and personal Sources method for finding raw data and supplementary materials.

E

• Effect Estimate: A statistical measure of the intervention effect, such as risk ratio, odds ratio, or mean difference.
• Effect Size: A quantitative measure of the magnitude of a phenomenon, such as the difference between two groups or the strength of an association.
• Eligibility Criteria: The predefined characteristics that studies must meet (inclusion criteria) or that disqualify studies (exclusion criteria).
• EMBASE: Excerpta Medica Database; a comprehensive biomedical literature database.
• EndNote: A commercial reference management software.
• Evidence Gap Map: A visual tool that highlights areas where evidence is lacking on a particular topic.
• Evidence Synthesis: The process of combining information from multiple research studies to provide a comprehensive understanding of what is known about a research question.
• Evidence Table: A structured summary of the characteristics and findings of included studies.
• Exclusion Criteria: The predefined characteristics that disqualify studies from inclusion in a review.

F

• Fixed-Effects Model: A statistical model used in meta-analysis that assumes all studies share a common true effect size.
• FAIR Principles: Guidelines for research data management ensuring data is Findable, Accessible, Interoperable, and Reusable.
• Forest Plot: A graphical representation of the results of a meta-analysis, showing effect estimates and confidence intervals for individual studies and the pooled effect.
• Full-Text Screening: The process of reviewing the complete text of studies to determine if they meet inclusion criteria.
• Funnel Plot: A graphical tool used to assess publication bias in meta-analyses by plotting effect size against study precision.

G

• Grade/GRADE: Grading of Recommendations Assessment, Development and Evaluation; a system for rating the quality of evidence in systematic reviews.
• Grey Literature: Research material produced outside traditional commercial or academic publishing channels, such as government reports, conference proceedings, and theses.

H

• Handsearching: The process of manually searching journals, conference proceedings, or other publications not indexed in electronic databases.
• Heterogeneity: The variation or differences among studies included in a review; can be clinical, methodological, or statistical.
• Hierarchy of Evidence: A framework that ranks study designs based on their internal validity and risk of bias.
• HIMS: Heterogeneity In Meta-analysis Software; a tool for analyzing between-study heterogeneity.

I

• I²: A statistical measure quantifying the percentage of variation across studies due to heterogeneity rather than chance.
• Inclusion Criteria: The predefined characteristics that studies must have to be included in a review.
• Information Specialist: A professional with expertise in developing comprehensive search strategies for systematic reviews.
• Intention-to-Treat Analysis: An analysis strategy where participants are analyzed according to their allocated treatment group regardless of adherence or protocol deviations.
• Individual Participant Data (IPD): Original, unprocessed data collected for each participant in a study.
• Interquartile Range (IQR): A measure of statistical dispersion, representing the range between the first and third quartiles.

J

• JBI Critical Appraisal Tools: A collection of checklists developed by the Joanna Briggs Institute for assessing the quality of studies with various designs.
• Journal Impact Factor: A metric reflecting the yearly average number of citations to articles published in a journal.

K

• Kappa Statistic: A measure of inter-rater reliability used to assess agreement between reviewers during study selection or quality assessment.
• Key Informant: An individual with specialized knowledge consulted during the development of a systematic review.
• Keywords: Terms used to search databases for relevant studies.

L

• Language Bias: Systematic error resulting from the exclusion of studies based on language.
• Literature Search: The process of identifying potentially relevant studies through systematic searching of bibliographic databases and other sources.
• Living Systematic Review: A systematic review that is continually updated as new evidence becomes available.
• Logic Model: A visual representation of how an intervention is expected to lead to specific outcomes, often used in realist reviews.

M

• MeSH Terms: Medical Subject Headings; a controlled vocabulary used for indexing articles in MEDLINE/PubMed.
• Meta-Analysis: A statistical technique for combining the results of multiple studies to produce a weighted average effect size.
• Meta-Bias: Biases that occur in the systematic review process, such as publication bias.
• Meta-Regression: A statistical technique used to explore relationships between study characteristics and effect sizes in meta-analyses.
• Methodological Quality: The extent to which a study's design, conduct, and analysis have minimized biases.
• Mixed Methods Review: A systematic review that combines both quantitative and qualitative evidence.

N

• Narrative Synthesis: A textual approach to data synthesis when meta-analysis is not appropriate.
• Network Meta-Analysis: A meta-analysis comparing multiple treatments simultaneously using both direct and indirect comparisons.
• NHMRC Levels of Evidence: A hierarchy of study designs used by the National Health and Medical Research Council (Australia).
• Non-Randomized Study: Research design where participants are not randomly assigned to intervention or control groups.
• Number Needed to Treat (NNT): A measure indicating the number of patients who need to receive an intervention to prevent one additional adverse outcome.

O

• Observational Study: A study where researchers observe and measure outcomes without intervening.
• Odds Ratio (OR): A measure of association between an exposure and an outcome, comparing the odds of exposure in those with the outcome to the odds in those without.
• Open Science: The practice of making research methods, data, and findings transparent and accessible.
• Outcome Reporting Bias: Systematic differences between reported and unreported findings, typically based on the nature and direction of results.

P

• P-value: A statistical measure indicating the probability of obtaining results at least as extreme as those observed, assuming the null hypothesis is true.
• P-hacking: The practice of manipulating data analysis to achieve statistically significant results.
• PECO Framework: Population, Exposure, Comparator, Outcome; a framework for structuring questions about etiology or harm.
• Peer Review: Evaluation of research by one or more experts in the field.
• PICO Framework: Population, Intervention, Comparator, Outcome; a framework for structuring clinical questions.
• PICOST Framework: Population, Intervention, Comparator, Outcome, Setting, Time; an extended PICO framework.
• PRESS Checklist: Peer Review of Electronic Search Strategies; guidelines for evaluating search strategies.
• PRISMA Statement: Preferred Reporting Items for Systematic Reviews and Meta-Analyses; a set of guidelines for reporting systematic reviews.
• PRISMA-P: PRISMA for Protocols; guidelines for reporting systematic review protocols.
• PRISMA Flow Diagram: A standardized flow chart depicting the flow of information through the different phases of a systematic review.
• PROSPERO: International prospective register of systematic reviews.
• Protocol: A detailed plan outlining the objectives, methods, and analysis for a systematic review.
• Publication Bias: Systematic differences between published and unpublished studies, typically related to the nature and direction of results.

Q

• Qualitative Evidence Synthesis: A systematic approach to reviewing and integrating findings from qualitative studies.
• Qualitative Research: Research that explores and understands the meaning individuals or groups ascribe to social or human problems.
• Quality Assessment: Evaluation of the methodological strengths and limitations of included studies.
• Quality of Evidence: The confidence that an effect estimate is correct, often evaluated using GRADE.
• Quantitative Research: Research that tests objective theories by examining relationships among variables.

R

• Random-Effects Model: A statistical model used in meta-analysis that assumes the true effect sizes vary across studies.
• Randomized Controlled Trial (RCT): A study design where participants are randomly assigned to intervention or control groups.
• Rapid Review: An accelerated systematic review that streamlines traditional methods to produce information more quickly.
• Realist Review: A theory-driven approach to synthesizing evidence with emphasis on understanding how complex interventions work in particular contexts.
• Reference Management Software: Tools (e.g., EndNote, Zotero, Mendeley) for organizing and managing references.
• Registration: The process of documenting a systematic review protocol in a registry such as PROSPERO before starting the review.
• Relative Risk (RR): A measure of the risk of an event occurring in one group compared to another.
• Research Question: The specific inquiry a systematic review aims to address, often formulated using frameworks like PICO.
• Risk of Bias: The likelihood that features of a study's design or conduct have introduced systematic errors that could affect the results.
• Risk of Bias Tools: Standardized instruments used to assess the potential biases in included studies (e.g., Cochrane Risk of Bias Tool, ROBINS-I).
• Risk Ratio: See Relative Risk.
• ROBINS-I: Risk Of Bias In Non-randomized Studies - of Interventions; a tool for assessing risk of bias in non-randomized studies.

S

• Sampling Bias: Systematic error resulting from the selection of a non-representative sample from a population.
• Scoping Review: A type of knowledge synthesis that maps the existing literature on a particular topic to identify key concepts, gaps in research, and types of evidence.
• Search Filter: A predefined search strategy designed to retrieve specific types of studies or information from a database.
• Search Strategy: A structured approach to searching databases, including keywords, subject headings, and boolean operators.
• Selection Bias: Systematic differences between baseline characteristics of the groups being compared.
• Sensitivity Analysis: A method to determine how robust the results of a systematic review are to changes in assumptions, methods, or data.
• Small-Study Effects: A tendency for smaller studies to show larger treatment effects, often indicating publication bias.
• SPICE Framework: Setting, Perspective, Intervention, Comparison, Evaluation; a framework for structuring research questions.
• SPIDER Framework: Sample, Phenomenon of Interest, Design, Evaluation, Research type; a framework for qualitative evidence synthesis questions.
• Standard Deviation (SD): A measure of the amount of variation or dispersion in a set of values.
• Standard Error (SE): A measure of the statistical accuracy of an estimate.
• Statistical Heterogeneity: Variability in the intervention effects being evaluated in different studies.
• Statistical Significance: A determination that an observed effect is unlikely to have occurred by chance alone.
• STROBE Statement: Strengthening the Reporting of Observational studies in Epidemiology; guidelines for reporting observational studies.
• Study Design: The methodology used to collect and analyze data to answer a research question.
• Subgroup Analysis: Analysis that explores whether effects of an intervention differ according to characteristics of studies or participants.
• Summary of Findings Table: A table presenting the main findings of a systematic review and the quality of evidence for each outcome.
• Systematic Review: A structured, comprehensive synthesis of research studies on a specific topic using explicit, reproducible methods.

T

• Thematic Analysis: A method for identifying, analyzing, and reporting patterns (themes) within qualitative data.
• TREND Statement: Transparent Reporting of Evaluations with Nonrandomized Designs; guidelines for reporting non-randomized studies.
• Triangulation: The use of multiple methods or data sources to develop a comprehensive understanding of phenomena.
• Trim and Fill Method: A statistical approach to adjusting for publication bias in meta-analyses.

U

• Umbrella Review: A systematic review of systematic reviews.
• Uncertainty: Lack of precise knowledge about the true value of a parameter.
• Unpublished Data: Research findings that have not been published in a peer-reviewed journal or other formal publication.

V

• Validity: The extent to which a concept, conclusion, or measurement is well-founded and corresponds accurately to the real world.
• Variable: A characteristic or attribute that can take on different values.
• Variance: A statistical measure of how far a set of numbers are spread out from their average value.

W

• Web of Science: A citation indexing service and scientific citation search engine.
• Weight: In meta-analysis, the relative contribution of each study to the overall pooled result.
• Weighted Mean Difference (WMD): A method of meta-analysis used when all studies measure an outcome in the same way.

Z

• Z-score: A statistical measurement of a score's relationship to the mean in a group of scores.
• Zotero: An open-source reference management software.