Evidence is a conception animatedly discussed, and many different understandings as to what counts as evidence in a socio-politic context are in existence. Below this, SFI Campbell elaborates on the term.

‘The best current knowledge’
Usually, a range of different considerations are taken into account when making a decision in which two different interventions and just one problem are at play. Actual reviews are rarely produced, even though it is this exact form of evidence that can estimate the effects of an intervention with most certainty.
 
Typically, there is a varying amount of other “evidence” or indications of what the best choice is. This may concern everything from the rule of thumb and gut feelings, over personal colleagues’ experiences, to evaluations of similar interventions.

Evidence is not just research-based knowledge
The best current knowledge is retrieved through systematic means. Going through the aquired knowledge thoroughly and critically shows that evidence can be differentiated, and that it is not always possible to retrieve the most substantiated evidence. In cases like this, for example expert statements, your own or your collegues' experiences, or maybe even random expectations or hunches will constitute the best current knowledge.

In this way, evidence is much more than what research tells us. Not all aspects have been explored and illuminated by the quality research.

Evidence cover a broader notion of knowledge than research, but evidence is also not limited to knowledge of effects. Effects are just one of the many notions which evidence based politics and pracsis would want to ask questions about in order to gain knowledge and evidence. The effect question is the question the international Campbell Collaboration thrives to provide the most qualified answer to - based on the best provided research.

Campbell Reviews are solid evidence
You get the most reliable answers from systematic and well-arranged effect studies. And even more so, if several surveys are brought together to give a more precise estimate of whether an intervention works or not.

Qualitatively, a systematic review is the best sort of evidence-based research because of the systematic work put into the reduction of possible sources of error that may cause an uncertainty about the conclusions drawn on the basis of of the contents of the review.