statistical designs

Case-Control Study Definition

Compares patients who have a disease (cases) to a similar group without the disease (controls) to identify past exposures or risk factors.

Case-Control Starting Point

Starts with the outcome (disease vs. no disease) and looks retrospectively backward at past exposure/risk factors.

Case-Control Benefits

Easy and quick to obtain data, less expensive than RCTs, and allows assessment of outcomes when exposing patients to an intervention would be unethical.

Case-Control Limitations

Cannot establish direct cause-and-effect (causality) and is susceptible to recall bias.

Cohort Study Definition

Compares outcomes between a group exposed to a treatment/risk factor and an unexposed group; can be followed prospectively or retrospectively.

Cohort Study Starting Point

Starts with the exposure status (exposed vs. unexposed) and follows groups over time to assess who develops the outcome.

Cohort Study Benefits

Allows assessment of risk factors and outcomes when active experimental intervention is unethical.

Cohort Study Limitations

Can be heavily influenced by confounding variables and is more expensive and time-consuming than case-control studies.

Cross-Sectional Survey Definition

Measures both the exposure/variable and outcome simultaneously at a single specific point in time within a defined population.

Cross-Sectional Primary Output

Estimates disease or trait prevalence in a population at a specific point in time.

Cross-Sectional Benefits

Useful for generating hypotheses and identifying associations that need further investigation.

Cross-Sectional Limitations

Does not determine causality or temporal sequence because exposure and outcome are measured at the same time.

Case Report vs. Case Series

A Case Report details a unique presentation/finding in a single patient; a Case Series describes findings across a small group of multiple patients.

Case Report/Series Benefits

Can identify novel diseases, unexpected adverse effects, or new off-label therapeutic uses, generating hypotheses for future studies.

Case Report/Series Limitations

Cannot draw definitive conclusions, determine incidence, or establish causality due to small sample size and lack of a control group.

Randomized Controlled Trial (RCT) Definition

An experimental study design that compares an intervention group to a control group, where participants are randomly assigned to minimize bias.

RCT Blinding Types

Double-blind (both patient and researcher are unaware of assignment), Single-blind (only patient is unaware), Open-label (both are aware).

RCT Benefits

Preferred gold standard for establishing cause-and-effect relationships with minimal potential for allocation and selection bias.

RCT Limitations

Extremely expensive, time-consuming, and may face ethical restrictions regarding experimental interventions.

Parallel RCT Design

Subjects are randomized to either the treatment arm or control arm and remain in that assigned group for the entire duration of the study.

Crossover RCT Design

Participants are randomly assigned to sequence groups that receive all treatments in a varied order, acting as their own controls.

Crossover RCT Key Advantage and Requirement

Minimizes individual confounding variables (since patients act as their own control), but requires an adequate washout period between treatments.

Factorial Design RCT

Randomizes subjects across two or more experimental factors simultaneously to test multiple interventions/conditions in a single trial.

Meta-Analysis Definition

A quantitative statistical method that combines numerical data from multiple independent studies to derive a single pooled conclusion with greater statistical power.

Systematic Review Definition

A comprehensive, standardized summary of scientific literature focused on a specific, narrowly defined clinical question.