Evidence and research methods
What a Negative Control Tells You
A negative control asks a related question whose causal answer should be null, helping reveal confounding, selection, measurement, or analytic bias.
Health & Evidence Library
Evidence and research methods
Tools for reading studies, interpreting tests and effect estimates, recognizing uncertainty, and asking whether evidence applies.
207 guides · Page 2 of 4
Evidence and research methods
What a Funnel Plot Shows, and What It Cannot
Learn how a funnel plot displays small-study effects, why asymmetry has several causes, and when visual or statistical tests are informative.
Evidence and research methods
What a Control Group Really Does
A control group estimates what would happen without the tested intervention and defines the comparison a study can legitimately claim.
Evidence and research methods
What a Confidence Interval Is Not
A confidence interval describes estimate precision under a model. It is not the probability that a claim is true or that one result will repeat.
Evidence and research methods
Vaccine Science: How Evidence Is Built Before and After Authorization
How laboratory work, clinical trials, regulatory review, recommendations, safety surveillance, and causal assessment fit together.
Evidence and research methods
The Win Ratio: Reading Hierarchical Composite Endpoints
How win-ratio analyses rank outcomes, compare patient pairs, handle ties and censoring, and sometimes hide which component drives a result.
Evidence and research methods
The Spectrum Effect: Why Test Accuracy Shifts With Case Mix
Sensitivity and specificity can change across severity, alternatives, settings, and pathways. Learn how spectrum effects alter diagnostic accuracy.
Evidence and research methods
The Limits of a Single Study
Why one study rarely settles a scientific question, how chance and bias shape results, and how replication and synthesis strengthen conclusions.
Evidence and research methods
The Imperfect Reference Standard Problem
Diagnostic accuracy is measured against a reference standard. When that standard makes errors, sensitivity and specificity can mislead.
Evidence and research methods
The Hierarchy of Evidence, Explained
Evidence hierarchies rank designs by the biases they usually control, but the right design depends on the question and quality still matters.
Evidence and research methods
The Fragility Index, Explained
The fragility index counts outcome changes needed to cross a significance threshold. It is intuitive, narrow, and easy to overinterpret.
Evidence and research methods
The File Drawer Problem
When studies stay unpublished because of their results, the visible literature can exaggerate benefits and hide uncertainty. Here is how to detect it.
Evidence and research methods
The Estimand Framework, Explained
An estimand states the exact treatment effect a trial seeks, including population, treatment, endpoint, later events, and summary measure.
Evidence and research methods
The Ecological Fallacy: Keep the Claim at the Level of the Data
Why associations among countries, counties, or hospitals cannot automatically describe the people within them, and when group data remain useful.
Evidence and research methods
The Counterfactual Idea in Causal Inference
Causal questions compare what happened with what would have happened under another action. Learn potential outcomes, assumptions, and target trials.
Evidence and research methods
Target Trial Emulation Explained
Target trial emulation starts with the randomized trial researchers wish they could run, then maps that protocol transparently to observational data.
Evidence and research methods
Surrogate Endpoints Versus Outcomes That Matter
A biomarker can shorten a trial without guaranteeing patient benefit. Learn validation, trial-level prediction, failure modes, and confirmatory evidence.
Evidence and research methods
Statistical Significance vs Clinical Importance
A p-value addresses compatibility with a statistical model. Clinical importance depends on effect size, uncertainty, baseline risk, harms, burden, and values.
Evidence and research methods
SPRINT: What Intensive Blood-Pressure Treatment Proved
SPRINT lowered cardiovascular events and mortality in selected high-risk adults. Learn its targets, measurement protocol, harms, and limits.
Evidence and research methods
Small-Study Effects: Egger's Test and Trim-and-Fill
Funnel-plot asymmetry can have many causes. Learn what Egger's test and trim-and-fill estimate, their assumptions, and safer interpretation.
Evidence and research methods
Single-Blind, Double-Blind, and Open Peer Review: What Trials Show
Randomized journal trials tested masked authors, signed reviews, and public reports. Their narrow results do not settle whether peer review works overall.
Evidence and research methods
Sensitivity and Specificity: A Practical Guide
Learn how sensitivity, specificity, predictive values, prevalence, thresholds, and likelihood ratios change the meaning of a diagnostic test.
Evidence and research methods
Sample Size for Developing a Prediction Model
The ten-events-per-variable rule is not enough. Learn how shrinkage, outcome frequency, predictor parameters, and precision guide model sample size.
Evidence and research methods
Risk Enhancers in a Statin Decision
How the 2026 dyslipidemia guideline combines PREVENT risk, risk enhancers, Lp(a), apoB, and coronary calcium in primary prevention.
Evidence and research methods
Restricted Mean Survival Time, Explained
Restricted mean survival time reports average event-free time through a chosen horizon and remains interpretable when hazards are not proportional.
Evidence and research methods
Research With Vulnerable Populations and Extra Protections
How research ethics turns contextual vulnerability into added safeguards while avoiding unjustified exclusion from evidence and benefits.
Evidence and research methods
Research Misconduct, Questionable Practices, and Honest Error
How current US policy distinguishes fabrication, falsification, and plagiarism from detrimental practices, disagreement, and honest error.
Evidence and research methods
Reproducibility Versus Replicability
A practical guide to computational reproducibility, new-data replication, terminology differences, and what each can and cannot establish.
Evidence and research methods
Reproducibility in Diabetes Research
A diabetes-specific guide to reproducible analysis, replication, assay harmonization, CGM definitions, transparent protocols, and data sharing.
Evidence and research methods
Reporting Guidelines, CONSORT 2025, and the EQUATOR Network
How CONSORT 2025 and the EQUATOR Network make health research checkable, and why complete reporting does not guarantee a sound study.
Evidence and research methods
Relative Risk Versus Odds Ratio
Relative risk compares probabilities; an odds ratio compares odds. They are similar for rare outcomes and can diverge sharply for common outcomes.
Evidence and research methods
Regression to the Mean in Health and Research
Extreme measurements often move toward average on repeat testing. Learn why this happens, how it mimics treatment benefit, and how studies control it.
Evidence and research methods
Reading the Esketamine Evidence for Treatment-Resistant Depression
What esketamine trials show about rapid symptom change, monotherapy, relapse prevention, masking, selected populations, safety, and regulatory limits.
Evidence and research methods
Reading Nonrandomized Studies With ROBINS-I
A practical guide to target trials, confounding, immortal time, result-level judgments, and the draft six-domain ROBINS-I V2.
Evidence and research methods
Reading an Objective Response Rate in a Cancer Study
How objective response rate is defined, measured, confirmed, and interpreted alongside duration, independent review, missing scans, safety, and survival.
Evidence and research methods
Reading a Trial That Missed Its Endpoint: The Lactate Question in Septic Shock
What ANDROMEDA-SHOCK tested, why its primary mortality result was negative, what the confidence interval permits, and how later evidence should be separated.
Evidence and research methods
Reading a Network Meta-Analysis and the Transitivity Assumption
How network meta-analysis combines direct and indirect comparisons, why transitivity is essential, and why treatment rankings can overstate certainty.
Evidence and research methods
Read Trials on the Pragmatic-Explanatory Continuum
Interpret pragmatic and explanatory trials by matching eligibility, setting, delivery, follow-up, outcomes, and analysis to the study purpose.
Evidence and research methods
Quantifying Heterogeneity: What I-Squared and Tau-Squared Each Mean
How I-squared, tau-squared, Cochran's Q, and prediction intervals describe different parts of between-study variation in a meta-analysis.
Evidence and research methods
QUADAS-2 and QUADAS-3: How to Judge Bias in Diagnostic Accuracy Studies
How QUADAS-2's four domains identify bias in diagnostic studies, and what changed when QUADAS-3 became the recommended version in 2026.
Evidence and research methods
Publication Bias in Antidepressant Trials: What the FDA Record Revealed
How Turner compared FDA records with journal articles, quantified selective publication, and showed why trial registries matter.
Evidence and research methods
Propensity Scores Explained: Balance, Overlap, and the Confounding They Cannot Fix
How propensity scores support observational comparisons through matching or weighting, and how to audit balance, overlap, and residual bias.
Evidence and research methods
PREVENT Equations Versus Pooled Cohort Equations: What Changed and Why
How PREVENT differs from the Pooled Cohort Equations in population, outcomes, inputs, race, kidney measures, time horizon, calibration, and guideline use.
Evidence and research methods
Prespecified Versus Post Hoc Analyses: How to Judge the Difference Fairly
How protocols, registries, and statistical analysis plans constrain flexibility, when deviations are legitimate, and why post hoc findings can still be useful.
Evidence and research methods
Prediction Model Impact Studies Versus Validation: The Evidence Gap That Matters
Why good predictive performance does not prove clinical benefit, and how impact studies test workflow, decisions, outcomes, harms, cost, and equity.
Evidence and research methods
Prediction Intervals in Meta-Analysis: What They Add Beyond a Confidence Interval
How prediction intervals describe between-study heterogeneity, why they differ from confidence intervals, and when their apparent precision can mislead.
Evidence and research methods
Precision Versus Accuracy in Measurement: A Clinical Research Guide
A practical guide to accuracy, trueness, precision, repeatability, reproducibility, bias, uncertainty, calibration, and traceability in clinical measurement.
Evidence and research methods
Post-Publication Peer Review: How Scientific Critique Continues After Publication
How comments, corrections, expressions of concern, and retractions work after publication, plus a practical method for weighing public criticism.
Evidence and research methods
Peer Review and Preprints: What Review Can and Cannot Catch
Peer review adds expert scrutiny but cannot certify truth, integrity, or replication. Learn how to weigh preprints, revisions, and corrections.
Evidence and research methods
One Health, Climate, and Health: A Framework for Connected Risks
How human, animal, plant, and environmental systems interact, how climate shapes health pathways, and how to interpret risk without overclaiming causation.
Evidence and research methods
NRI and IDI Reclassification Metrics, and Their Pitfalls
NRI and IDI can describe changes between prediction models, but calibration, thresholds, optimism, and clinical utility determine whether changes matter.
Evidence and research methods
Missing Trial Data Are an Assumption Problem, Not an Empty-Cell Problem
Missing trial outcomes can change an estimate when absence relates to health or treatment. Imputation and sensitivity analyses make assumptions visible.
Evidence and research methods
Meta-Research Measures How Science Is Produced, Checked, and Rewarded
Meta-research studies research methods, reporting, verification, evaluation, and incentives so scientific reform can be tested with evidence.
Evidence and research methods
Meta-Regression Explains Differences Between Studies, Not Between People
Meta-regression relates study features to effect estimates, but ecological bias and sparse study counts limit individual-level conclusions.
Evidence and research methods
Medication Safety and Adherence: A Practical System for Safer Use
How medication lists, reconciliation, interaction checks, barrier-aware adherence support, and clear follow-up reduce preventable harm.
Evidence and research methods
Mediation Analysis Tests a Pathway, but the Pathway Is Not Randomized
Mediation analysis separates direct and indirect effects, but causal interpretation depends on timing, measurement, and confounding assumptions.
Evidence and research methods
Is This Systematic Review Still Current?
Judge systematic review currency from its last search, new evidence, current question, methods, certainty, and update process.
Evidence and research methods
Individual Participant Data Meta-Analysis: What the Raw Records Add
How IPD meta-analysis checks and harmonizes participant records, preserves trial structure, studies effect modifiers, and handles missing data sets.
Evidence and research methods
How Trials Report Harms, and Why the Safety Half Is Often Thin
How to appraise event definitions, collection, denominators, recurrence, time at risk, withdrawals, coding, missing data, and rare harms in trials.
Evidence and research methods
How to Read Image-Integrity Concerns in Research Papers
How duplicated, spliced, or selectively adjusted figures are detected, investigated, and interpreted without assuming intent.