studydesign

Study design refers to the framework used to collect, measure, and analyze data to answer a specific research question. It encompasses decisions about how participants are selected, how and when data are collected, and how variables are defined and measured. Study designs are generally categorized as experimental (or interventional) and observational, and may be quantitative or qualitative.

In experimental designs, the researcher intervenes and assigns exposure or treatment. Randomized controlled trials are the gold standard for assessing causal effects, using random allocation to intervention and control groups, with blinding where feasible and concealed allocation to reduce bias. Other experimental approaches include factorial designs, where multiple factors are tested, and cross-over designs, where participants receive multiple treatments in sequence.

Observational designs observe exposures and outcomes without random assignment. Cohort studies follow groups over time, case-control studies compare individuals with and without an outcome, and cross-sectional studies assess exposure and outcome at a single time point. Qualitative study designs explore phenomena through methods such as interviews and ethnography and emphasize depth over generalizability. Mixed-methods designs combine quantitative and qualitative strands.

Key design considerations include validity and bias: internal validity (risk of confounding, measurement error) and external validity (generalizability). Sample size and power influence the ability to detect effects. Ethical approval, informed consent, and preregistration improve transparency. Reporting guidelines such as CONSORT for trials, STROBE for observational studies, and PRISMA for systematic reviews guide clear presentation of methods and results.