duration of study

Last reviewed 01/2018

Study duration

  • duration of the study needs to be sufficient to allow those events to occur in the given sample of subjects
    • if the period for study follow-up is too short then too few events may occur to enable detection of any difference between interventions
    • if the period of study follow-up is of limited duration then this raises concerns about interventions that could ultimately be used chronically in patient populations
      • results of clinical studies of limited duration cannot provide information on the longer-term effects of treatment
      • clinical studies of limited duration cannot provide information about relatively rare adverse effects
    • note though that occasionally a clinical study will be terminated earlier than planned because one of the interventions has demonstrated significant benefits or ill-effects compared with its comparator. In this situation it may be considered unethical to continue to withhold treatment with an intervention from those people who have been treated with an inferior comparator in the study. Note thought that an early termination of the study limits the information available on longer-term effectiveness and side effects of the intervention of interest


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  2. Best Pract Res Clin Obstet Gynaecol. 2005;19(1):15-26.
  3. Wiebe S. The principles of evidence-based medicine.Cephalalgia. 2000;20 Suppl 2:10-3.