C – Comparator: comparison or control

What is the intervention being compared to?

Now that you have defined your population and intervention of interest, you need to consider your choices (i.e. what the intervention will be compared to)

The PICO framework allows you to consider quite a wide range of interventions, from considering a new treatment, to examining the impact of a particular exposure to a risk factor, to determining how prognostic a certain test might be.

It is important to realise that any intervention needs to be considered at the same time as a comparator, as without a comparison it is difficult to evaluate the impact of the particular treatment, prognostic factor or exposure you are interested in. The PICO framework considers the treatment, clinical sign or exposure of interest to be the intervention with which we are concerned, and considers an alternative to be the comparator.

If we are evaluating a specific therapy, for example, we would choose that therapy as the intervention, and we wish to find evidence comparing its efficacy with alternative comparators or control treatments. When dealing with a question of diagnosis, however, we may wish to find evidence describing how the consideration of a specific diagnostic test or clinical sign increases our diagnostic accuracy compared to an alternative (a control).

And when considering a question of aetiology or harm, we may wish to discover the association between a risk factor or exposure and the occurrence of disease.

Question Comparator
Which diet is best to feed cats with chronic renal disease? Not feeding a renal prescription diet
Which diagnostic test is most reliable for diagnosing fascioliasis in dairy cattle? Serum ELISA
Does sex affect survival in flat-coat retrievers with cancer? Being female
What are the risks of general anaesthesia in ferrets? General anaesthesia by induction and inhalational agent
What is the prevalence of cardiac disorders in Welsh Section A mountain ponies? Being any other breed of horse