In this presentation I want to share my experience with writing a systematic review.
I recently published a systematic review in Earth-Science Reviews along with my colleague Joris de Vente, in which we studied the impact of climate change on soil erosion, with an extra focus on conservation measures and land use change.
We collected more than 30 variables from 224 papers, which varied among bibliographic variables, study area characteristics and, most importantly, methodological variables.
We included a statistical analysis of these methodological variables and asked through an online questionnaire the opinion on the robustness of these methodologies, more on this questionnaire later on in the presentation.
From the results of the questionnaire we obtained robustness scores, which we translated to weights per study and determined weighted statistics. We show that soil erosion is projected to increase under climate change, with an increasing trend towards the end of the century.
The process that led to the systematic review started in 2018 with the two studies focusing on methodologies used in climate change impact assessments, first focusing on bias-correction methods and climate model ensembles and later on soil erosion model conceptualization.
In both cases we had some thoughts about common methods used, but wanted to have a better foundation from the literature. So we started collecting data from SCOPUS.
We published the preliminary databases along with these two publications as supplementary material. With this I want to show that it is useful to start small with a specific question and work your way towards a systematic review in a few years.
While writing the systematic review we used the SALSA framework, which is a structured and contextual approach widely used for systematic literature reviews. It consists of four steps, Search, Appraisal, Synthesis and Analysis, which I will discuss in the following slides.
In the first step, Search, you need to define the research scope, which defines clear boundaries for your study and which you can base on another framework called PICOC.
Next you can define the research questions, which go into more depth of the subject of your study.
This is followed by the search term. Our search term consisted of two parts. The first part on 'soil erosion' and related terms applied to the title, abstract and keywords, and the second part on 'climate change', which was only applied to the title.
Once you have formulated the search term you can go to SCOPUS or WOS and download the resulting table and you can follow with the next step: Appraisal. In this step you need to define criteria to include and exclude publications.
In the third step, Synthesis, you need to define the variables you want to focus on. We included a table in the SI of our paper, in which we described all the variables, including some categorical variables, such as the study size classes.
In the last step, Analysis, you need to write a short paragraph on how the data from the papers are used to draw conclusions. For instance, if some statistics or other methods are applied on the data extracted from the papers.
Many systematic reviews include figures like this, to show how many papers have been published per year. But you can also go a bit beyond such bibliographic analysis, which is what we did by extracting author information from the database.
We wanted to know the opinion of fellow scientists on our subject and made an online questionnaire, which we sent to the most common authors in the database. 19 authors filled in the questionnaire, which helped us a lot to quantify uncertainty in our study.
In the last slide I want to show something about the impact of our study. While it is only recently published, some results were included in two IPCC reports that I have reviewed, from which one I was asked to become contributing author.
In the second IPCC report, many suggestions from my review were included in this paragraph. With this I want to show that your systematic review can be very useful for policy reports and can have an impact beyond the scientific community.