For today’s post, you might want to open a second window at the Cochrane Collaboration Website so you can scroll through what is available while we talk. One thing I have been trying to communicate (over and over and over) is that each study is only one small piece of the puzzle researchers use to help figure out what is going on. Today we are going to talk about one tool researchers use to synthesize the available data, the Systematic Review.
So what exactly is a systematic review? It is a type of research where the data analyzed is other published research. Actually, there are lots of types of studies or reviews you can do that use existing research as the data. What sets a systematic review apart is the rigor. Think about how much work it takes to research and write an essay on any topic. Now think about how much more difficult that essay would be to write if you were expected to have made sure you analyzed every existing piece of research on that topic and you can pretty much see why writing a systematic review is difficult.
To start, the researchers must write a very specific question that defines their review. The specificity is what makes the review possible, and part of what makes multiple reviews on similar topics necessary.
Just like with a human study, researchers must define inclusion and exclusion criteria. For example, look at this study: Prostaglandins for management of retained placenta. In this review, the researchers only wanted studies that were randomized controlled trials of prostaglandins for a very specific use — retained placenta. In areas of research with more studies available the criteria might include specific outcomes. If there were already several randomized controlled studies on prastaglandins for retained placenta the authors might have refined their question to only deal with the effects on blood loss with retained placenta. The researchers would then limit themselves to studies that measured blood loss as a major outcome.
Once they have the question and the study criteria the researchers can begin searching for studies to include. This means searching multiple data bases, reading through abstracts and hand selecting which studies actually provide information for answering the question. This search process is carefully documented, with the reasons for excluding articles reported in the final review.
After selecting the appropriate studies, the researchers must assess the quality of each study. Then, and only then can they make conclusions about the findings.
It is a long process, but provides important information to both the research community and midwives. Systematic Reviews allow us to understand what is known from multiple studies, and helps us to identify areas that have not been well studied. This makes them useful tools for evidence-based practice and key documents for midwives who participate in writing protocols.
Next time we will talk about another type of study that synthesizes study results, the Meta-Analysis.