Study Types

Quantitative Research

Often called the “traditional method,” it involves testing theories using numbers. The researcher manipulates an independent variable to determine its effect on a measured dependent variable, often seeking to establish a cause-and-effect relationship.

Qualitative Research

This approach tests theories using language rather than numbers. It focuses on broad descriptions and understanding complex phenomena through interviews and thematic analysis of experiences and attitudes. Participants are typically selected purposefully rather than randomly

Quantitative Designs (by Bias Control)

Studies are ranked based on their ability to minimize bias—systematic deviations from the truth caused by uncontrolled influences

Experimental Designs (True Experimental/RCT)

These aim to demonstrate a cause-and-effect relationship by randomly assigning participants to two or more groups and purposefully manipulating an independent variable. The Randomized Controlled Trial (RCT) is the gold standard for maximizing internal validity

Quasi-Experimental Designs

These maintain controlled manipulation of the subjects but lack randomization or a second comparison group

Single-System (Single-Subject) Design

A type of quasi-experimental design where one subject (or a few) receives both experimental and control conditions in an alternating fashion to understand a process or a novel intervention

Nonexperimental (Observational) Designs

These lack controlled manipulation. Group assignment is predetermined based on naturally occurring characteristics, such as a specific diagnosis or age.

Physiologic (Basic Science) Studies

Highly controlled laboratory research focused on cellular, anatomic, or physiologic systems rather than person-level function

Case Reports

Detailed descriptions of the clinical management of a single unusual case or an infrequently encountered condition

What are timing and duration designs?

Prospective, retrospective, cross-sectional, longitudinal

Prospective Design

Researchers collect new data in real time by following subjects forward over a specified period

Retrospective Design

Researchers use historical (past) data from sources such as medical records or insurance claims

Cross-Sectional Study

Data is collected about a phenomenon at a single point in time or once within a single defined interval

Longitudinal Study

A phenomenon is studied over an extended period of time to observe changes (e.g., following a patient for a year after surgery)

Secondary (Pre-Appraised) Evidence

These sources summarize and appraise groups of primary studies to provide definitive answers.

Systematic Review

A method where a collection of individual studies is gathered and critically appraised to reach an unbiased conclusion about the cumulative weight of evidence on a topic

Meta-Analysis

A systematic review that includes a statistical component by combining data from multiple studies to present an overall result

Clinical Practice Guidelines (Summaries)

Systematically developed statements that include recommendations intended to optimize patient care, informed by systematic reviews and expert opinion.

Narrative Review

A description of prior research without a systematic search strategy or critical appraisal of study merits

What are specialized study types?

Diagnostic accuracy, methodological study, outcomes research

Diagnostic Accuracy Study

Determines how good a particular "index test" is at detecting a condition compared to a "reference standard" (gold standard).

Methodological Study

Any research study that investigates the reliability and/or validity of clinical and research measures

Outcomes Research

Focuses on the "actual results" of implementing care, such as improvements in function, participation, or quality of life

Qualitative Research Hierarchy

Level I: Generalizable Studies

Level II: Conceptual Studies

Level III: Descriptive Studies

Level IV: Single Case Study

Level I: Generalizable Studies

Comprehensive studies using theory-focused sampling to capture a diversity of experiences

Level II: Conceptual Studies

Use theoretical concepts to guide sample selection, often focused on a specific group.

Level III: Descriptive Studies

Samples are selected to illustrate practical issues, often using quotes to represent themes

Level IV: Single Case Study

Provides rich data on the unique experiences of one person.