The word evidence synthesis may not be the most thrilling word you can come up with. Nevertheless, it is an important word that everyone should know about. Here is why.
There is a stacking amount of scientific research being published every year. In fact, a study by the University of Ottowa from 2015 showed that there are approximately 2.5 million new articles being published every year. That’s a lot, and it goes without saying that such abundance of literature, makes it more or less impossible for you to get an overview of the evidence, if you simply choose to do a quick google search for literature published within your field of interest.
So that’s point 1: There is so much literature out there, that chances are you are missing out on some of it
Nevertheless, from time to time individual articles stand out in the crowd, due to their spectacular or worrying results. These individual articles may essentially be an eyeopener and set the stage for changing the clinical practice. They make the scientific community and lay public aware, that research has showed us something, that we did not anticipate. This essentially shows the value of conducting research – it allows us to see things that may not initially be obvious to our naked eye. However, when we choose to only focus on one paper, we get blindsided to what else may be out there. Chances are that there might be research telling the opposite story. Furthermore, reproducibility is key. Having one paper stating some incredible results, is not enough to make compelling conclusions and consider these results a law of nature. You need to be sure that other people are able to conduct the same research and come up with the same results. If not – then you seriously have to reconsider how much you believe in the results from that one paper getting the media attention.
Here is point 2: One paper stating incredible results is not enough to make compelling conclusion. We need to be sure that these incredible results can be reproduced. Otherwise they might be a false lead.
So how to check for all of this? Go look for systematic reviews. The essence of systematic reviews is to provide you with an overview of all the research that has been conducted so fare within a specific. As such, given that a proper systematic search and study selection has been conducted – you can rest ashore that you are most likely not missing out on important research. If you then combine this with a meta-analysis, you get the possibility to quantitively assess whether studies investigating the same thing, also end up having the same results. However – note of caution. This is all very good, but the results of the review are only as good as the method being used to construct them. In other words, you need to be sure that you are dealing with well-performed review before trusting the data. Otherwise, chances are that you still end up having distorted results.
Finally, point 3: Systematic reviews are a powerful tool, when constructed well.
There you have it, this is evidence synthesis for you. Evidence synthesis is simply the combination of all the research being done within a field. When performed well, it allows us to truly evaluate the overall benefits and harms of a given intervention.
That was a long story – want to see it in pictures? Then have a look at this great video from Cochrane.