In association with

  • Bristol, North Somerset and South Gloucestershire Clinical Commissioning Group Research and Evidence Team
  • West of England Academic Health Science Network



Observational study

A family of studies in which investigators compare people who take an intervention, with those who do not. The investigators neither allocate patients to receive the intervention nor administer the intervention. Instead, they compare records of patients who took an intervention and have been treated in routine practice, with similar patients who had not taken the intervention. The most common observational designs are case-studies, case-series, case-control studies, cohort studies, and historically-controlled studies. (Howick)


A ratio of events to non-events. If the event rate for a disease is 0.2 (20%), its non-event rate is 0.8 and therefore its odds are 2/8.