ABSTRACT
When discussing the validity of clinical trials, we need to consider both internal validity and external validity. Internal versus external validity is a distinction made in clinical epidemiology to discuss how well a clinical study answers certain questions. In broad terms, a study has high internal validity if the results can be considered accurate for the sample included in the study. It is an assessment of whether the study’s design and conduct is suffi cient to reliably answer the research question posed in the study. In clinical drug development, a study with high internal validity is considered to provide a reliable answer to the question: what is the effect of giving drug A to the sample studied in the trial? External validity, by contrast, refers to how well the outcomes observed in the study apply to people outside the sample included in the trial. When most people discuss internal and external validity, they do so in terms of randomized controlled trials , also known as RCTs or simply randomized trials . A common claim is that well-conducted randomized trials have better internal validity than other types of medical studies such as observational studies.
