A/B Testing
A/B testing is an experimental design that randomly assigns participants or users to one of two variants, labeled A and B, to compare their effects on a predefined outcome.
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Study Design Terms
How studies are planned before any data are collected: randomized trials, cohort and case control studies, quasi experiments and more. Learn what each design can and cannot show, and how randomization, blinding and control groups protect a study from bias.
A
Adaptive Design
An adaptive design is a clinical trial design that allows for prospectively planned modifications to one or more aspects of the trial based on accumulating data from participants, without undermining the study's integrity or validity.
Allocation Concealment
Allocation concealment is a procedural safeguard used in clinical trials to prevent the person enrolling participants from knowing or predicting the upcoming treatment assignment until the moment of allocation.
B
Before and After Study
A before and after study, also known as a pre post study, is a research design that measures outcomes in the same group of participants or settings before and after an intervention is implemented, without a separate contemporaneous control group.
Blinding
Blinding, also called masking, is a procedural safeguard in which study participants, investigators, outcome assessors, data analysts, or other parties are kept unaware of treatment assignments to prevent knowledge of the assigned intervention from…
C
Case Control Study
A case control study is an observational research design that compares individuals who have a specific disease or outcome (cases) with individuals who do not (controls) to identify factors associated with the occurrence of the outcome.
Clinical Trial
A clinical trial is a prospective research study that assigns human participants to one or more health related interventions to evaluate their effects on clinical outcomes.
Cluster Randomized Trial
A cluster randomized trial is a type of randomized experiment in which randomization occurs at the group level rather than at the individual level.
Cohort Study
A cohort study is an observational research design that follows a group of individuals who share a common characteristic or exposure over time to determine how certain factors affect the incidence of outcomes.
Comparative Study
A comparative study is any research design that compares two or more groups, interventions, conditions, or time periods to identify similarities and differences in outcomes, characteristics, or processes.
Control Group
A control group is the set of participants in an experimental study who receive either no intervention, a standard treatment, or a placebo, providing a baseline against which the effects of the experimental intervention are measured.
Cross Sectional Study
A cross sectional study is an observational design that examines a defined population at a single point in time or over a short period, measuring exposure and outcome simultaneously.
Crossover Trial
A crossover trial is a clinical trial design in which each participant receives both the experimental treatment and the control treatment in a predetermined sequence, usually separated by a washout period.
D
Descriptive Research
Descriptive research is a research approach that systematically observes and records the characteristics of a population, phenomenon, or situation without manipulating any variables.
Diary Study
A diary study is a longitudinal research method in which participants record their experiences, behaviors, symptoms, moods, or activities in real time or near real time over a defined period, typically ranging from several days to several weeks.
Double Blind
A double blind study is a research design in which neither the participants nor the researchers who interact with them, deliver the intervention, or assess the outcomes know which treatment group each participant has been assigned to.
E
Ecological Study
An ecological study is an observational research design in which the unit of analysis is a group or population rather than an individual.
Enrichment Design
An enrichment design is a clinical trial strategy that uses one or more preliminary steps to select patients in whom a treatment effect, if present, is more likely to be detected, then randomizes only those selected patients to receive the treatment or…
Equivalence Trial
An equivalence trial is a clinical trial designed to demonstrate that two treatments produce outcomes that are sufficiently similar, within a predefined margin of clinical acceptability, that neither is meaningfully inferior or superior to the other.
Ex Post Facto Research
Ex post facto research is a non experimental study design in which the researcher examines how an independent variable, one that has already occurred or cannot be manipulated, affects a dependent variable.
F
Factorial Design
A factorial design is an experimental design in which two or more independent variables (called factors) are manipulated simultaneously, allowing researchers to examine both the individual effects of each factor (main effects) and the combined effects of…
Feasibility Study
A feasibility study is a preliminary investigation conducted to evaluate whether a proposed research project, clinical trial, or intervention can be carried out as planned.
L
O
Observational Study
An observational study is a type of research design in which investigators observe participants without assigning treatments, exposures, or interventions.
Open Label Study
An open label study is a clinical trial design in which both the investigators and the participants know which treatment each participant is receiving.
P
Phase I Trial
A Phase I trial is the first stage of testing an experimental treatment in human subjects, primarily designed to evaluate the safety, tolerability, pharmacokinetics (how the body processes the drug), and pharmacodynamics (how the drug affects the body) of…
Phase II Trial
A Phase II trial is a clinical study that evaluates the efficacy and safety of an experimental treatment in patients with the target disease or condition.
Phase III Trial
A Phase III trial is a large scale, randomized, controlled clinical study designed to provide definitive evidence of the efficacy and safety of an experimental treatment compared to the current standard of care or placebo.
Phase IV Trial
A Phase IV trial, also called a post marketing study, is a clinical study conducted after a drug or other intervention has received regulatory approval and is available for clinical use.
Pilot Study
A pilot study is a small scale, preliminary investigation conducted before a full scale study to test the feasibility, procedures, instruments, and methods that are planned for a larger project.
Placebo
A placebo is an inert or inactive treatment that is designed to resemble the experimental intervention in appearance, administration, and sensory characteristics but contains no active therapeutic ingredient.
Pre Post Design
A pre post design is a quasi experimental study design that measures an outcome before and after an intervention in a single group of participants, without including a concurrent control group.
Q
R
Randomization
Randomization is the process of assigning study participants to different groups (such as treatment and control) using a chance mechanism, ensuring that each participant has a known, typically equal, probability of being placed in any group.
Randomized Controlled Trial (RCT)
A randomized controlled trial is an experimental study design in which participants are randomly assigned to receive either the intervention being tested or a control condition (such as placebo, standard treatment, or no treatment).
Regression Discontinuity
Regression discontinuity (RD) is a quasi experimental research design that estimates causal effects by exploiting a known threshold or cutoff on a continuous assignment variable that determines treatment eligibility.
Research Design
Research design is the overall strategy, framework, and structure that a researcher uses to address a research question, encompassing the type of study (experimental, observational, or qualitative), the data collection methods, the sampling approach, and the…