Applicability and relevance of the evidence

Even if the evidence is strong, with significant, precise, consistent and plausible results, it may not be useful to all those reading your review. Clinicians and consumers, looking for evidence about the best way to deal with an individual health care situation, will not only need evidence which is strong, they will need to know if it applies to them and is relevant to their clinical need.

Section 9.2 of the Reviewers Handbook discusses Applicability, or Relevance, and you should read it now.

Don't forget that the results of your review may be used in many different populations and settings around the world. Care needs to be taken not to interpret your review only as it applies to your own setting. Reviewers should try to help the reader in applying the results of their review to individual settings.

A useful way of doing this is to ask yourself if there are any reasons why the results of your review may be different if the intervention was used in a different setting. Some examples may be:

• Biologic and cultural variation

  There may be genetic reasons why an intervention may have varying effects in different populations with varying risks and co-morbidities. There may be gender or age differences in response to the treatment, or the intervention may simply not be feasible or acceptable in a given setting.

• Variation in baseline risk

  If all the trials in your review include populations with a similar baseline risk of the outcome (i.e. control event rate), while this may strengthen the evidence for the effect of the intervention in such populations, it may limit the applicability of the results.In asking whether the review is relevant, the issue is whether or not the evidence matters. In some cases interventions are assessed only by their effect on outcomes that are not important to the people with the disorder. Take the example of antiviral regimes for people living with HIV. If a review were only to report the effect of the regime on CD-4 count, and not include relevant outcomes such as health related quality of life, adverse drug effects or survival, the review may not be relevant to people living with HIV, although it may be helpful to their physician.

A relevant review is one that asks a sensible question. A review, or indeed a trial, that assesses the effect of an intervention compared to placebo when there is a proven effective treatment which can be used is clinically irrelevant. What we need to know is whether the new intervention is better than the existing proven intervention. You may chose to include trials comparing the new intervention to placebo in your review in order to draw an indirect comparison (as discussed in Module 14, Further Considerations In Meta-Analysis), however the primary question of your review should be to determine effect compared to the existing intervention.

Summary

In conclusion, when writing the Discussion section of your review you need to consider not only how convincing the evidence is in terms of the effect of the intervention, but also how this evidence will help in the many clinical settings in which people will wish to apply it.

The following Modules will discuss making conclusions from your review with respect to trade-offs between benefit and harm, and ways of expressing uncertainty.