Effect Size
A quantitative measure of the magnitude of a treatment effect, independent of sample size. Common measures include Cohen's d, odds ratio, and number needed to treat (NNT).
In Depth
Effect sizes allow comparison of treatment effects across studies with different sample sizes and outcome measures. In cannabis research, effect sizes for pain relief are typically moderate (Cohen's d 0.4–0.6), comparable to other analgesics. Effect sizes for CBD in epilepsy are large (50%+ seizure reduction in Dravet syndrome). Statistical significance (p-value) does not indicate clinical significance — a large trial can detect a statistically significant but clinically trivial effect.
Related Terms
More in Research Methods
Randomized Controlled Trial (RCT)
The gold standard study design in clinical research. Participants are randomly assigned to treatment or control groups to minimize bias and establish causation.
Systematic Review
A structured synthesis of all available evidence on a specific research question, using predefined criteria to identify, evaluate, and summarize studies.
Meta-Analysis
A statistical technique that combines quantitative data from multiple studies to produce a pooled estimate of effect size with greater statistical power than any individual study.
Placebo-Controlled
A study design in which the control group receives an inert substance (placebo) identical in appearance to the active treatment, to account for the placebo effect.
Observational Study
A study in which researchers observe participants without intervening. Includes cohort studies, case-control studies, and cross-sectional surveys.