Scope versus volume of evidence
The ACQUIRE section, coming next, explains more fully how you can use your PICO question to find the evidence.
Sometimes the question you ask may yield too much or too little relevant evidence. For example, you may find that your PICO has only yielded two papers, neither of which entirely answers your question. Assuming your search was conducted thoroughly, this may mean there is not enough evidence available to answer your question.
In veterinary medicine, we often deal with this problem of a dearth of evidence, and, in order to conduct an extensive search, it may sometimes be helpful to broaden the question you are asking or to search for evidence available in other species to make sure you haven’t missed any useful evidence. In doing this, however, you must take care to only use the evidence that directly answers your question of interest, and not be dragged away by other interesting papers which might not answer your clinical question.
Conversely, you may find that your search yields dozens and dozens of results, not all of which specifically relate to the problem or question you have in mind. In this case, it might be necessary to adjust your PICO to be more narrow and focussed, in order to distil only the most relevant evidence to answer your question. How you implement the evidence into practice will be further covered in APPLY and ASSESS.
Choice of interventions and comparators
It is unlikely that all the evidence you obtain will address all the treatments or diagnostic choices that exist for the problem you have chosen. Similarly to adjusting the scope of problem, you may need to refine your selection of treatment choices by excluding or modifying them. Sometimes the treatments you wish to compare have simply not been directly compared in the literature.
Although this is disappointing, it can lead to identifying research gaps that someone (perhaps you!) needs to answer. If you run into a situation where the specific treatments of interest have not been trialled, you may be forced to select the most similar treatments you can find with available information about their use, and then use your clinical judgement to interpret the results of the trials.
Sometimes, a clear choice for your patient will only have a single objective desirable outcome, and it is certainly nice when this is the case in your clinical question. In reality, however, veterinarians often want to investigate a number of different outcomes for ourselves, our clients and our patients. For example, we may wish for a treatment that is effective, easy to use and economic, all at once.
However, many studies in the literature may address multiple outcomes, looking at both efficacy (e.g. survival times) and negative outcomes (e.g. adverse events) as well as costs, all in the same study. Sometimes you may need to look across multiple studies to gather these data; to do this, you will effectively be asking a series of PICO questions, all with different outcomes. One strategy is to refine your outcome to be a composite statement that reflects your overall aims for a case (e.g. ‘long-term survival whilst pain free’).