CA - SR - Applicability
Systematic reviews have the potential to be the highest level of evidence about a given clinical topic, but only if:
they are performed well (the validity issues mentioned above)
they include high quality evidence themselves.
Be careful about drawing conclusions from systematic reviews. Importantly, learn to distinguish the difference between:
Proof of absence - the high quality review found high-quality evidence that, when pooled, shows no overall difference between the intervention and the control.
Absence of proof - the high quality review found TOO LITTLE high-quality evidence to make a determination about the effect of the intervention.
Heterogeneity - sometimes the discussion of heterogeneity in the review gives a clue about the applicability of the findings.
If the review finds that the intervention works when the studies done in a certain population are excluded, then you know not to try to apply that evidence in that population.
Similarly, if the review shows an intervention is effective, but only contains evidence about a certain population,the heterogeneity statistics might be reassuring, but the review's should generally be limited to the population studied.
General questions about APPLICABILITY are the same as those for a therapy question:
Is my patient like the patients in the review (look at inclusion and exclusion criteria)?
Is the intervention feasible in my practice?
Is the outcome one my patients would care about (patient-oriented evidence)?
Other Systematic Review Things
More on systematic reviews
Review CEBM Toronto's site on critical appraisal of systematic reviews
Network Meta-Analysis
Link to example article: http://onlinelibrary.wiley.com/doi/10.1111/bjd.12343/full
Validity Issues:
http://www.bmj.com/content/346/bmj.f2914