The aim of a clinical trial is sometimes to investigate the efficacy of an intervention in patients with a particular disease or condition. When performing a trial, it is impossible to enroll every patient with the particular disease or condition – instead, a sample of patients is selected that represents the population of interest. Essentially, the findings from the trial should have relevance to
patients in future clinical practice, i.e., the study should have
external validity or generalizability.
Some of the basic considerations for design in clinical trials are:
- Patient selection
- Sample size determination
In order to ensure generalizability:
- It is essential to have an understanding of the disease and its current treatment options.
- The selected sample must truly reflect the population it represents,
and the eligibility criteria must not be so restrictive that they
hamper recruitment or limit the generalizability of the findings.
However, eligibility criteria also serve the function of choosing a sample who can tolerate being in a trial and those in whom there are less co-morbidities that might dilute the effect of the intervention.