Dear all, I am conducting an Epidemiological systematic review and MA, during my search of database I found some 10 studies in PubMed, EMBASE, MEDLINE, Science Citation Index.
Additionally, while searching google scholar I also found many articles related to my review questions but their quality arent good.
So, please help me. Should I include or exclude them? What about Publication bias?
Thank you all in advance for your time
Hi Balamurugan janakiraman, there is no any difference among sources listed in Pubmed and Google scholar. You may include all sources to have a thorough literature review.
You should search all databases either pubMed or google scholar so that more and more studies can be included in the systematic review. But, the quality of all articles should be checked via appropriate scale and only good quality articles should be considered for final interpretation.
Dear Balamurugan, I differ from above 3 answers. The main purpose of systematic review is reproducibility of quality articles which will be compromised in great extent when we use GoogleScholar. When we use search strategy for google scholar it usually gives more citations than other search engines which will be very difficult to screen. But we (I) can use two instances:
1. Using last three years filters and screen the references of eligible articles
2. Use the most cited articles which may be quality article in most cases and found the citations history
3. Best to avoid it (I rarely found its name in quality journal SROL articles)
In order to select good quality articles, one of the inclusion criteria could be: articles published in scopus/web of science/pubmed-indexed journals only.
Hi Balamurugan,
A systematic review constitutes synthesis of the relevant literature on the concerned topic and the authenticity of its findings is highly dependent on the quality of the articles included in it. Therefore, I would suggest not to include google scholar as one of the search engine for retrieving articles for your review. It would be better to search in scopus/pubmed/ web of science/SCI/CENTRAL for retrieving good quality articles.
Publication bias occurs when the outcome of an experiment or research study influences the decision whether to publish or otherwise distribute it. Publishing only results that show a significant finding disturbs the balance of findings, and inserts bias in favor of positive results. Including google scholar as a search engine may not directly affect publication bias but it will definitely compromise the quality of your systematic review. You can test publication bias for your meta-analysis using funnel plot and egger's test.
Following links on search engines to include in a systematic review and publication bias may help you:
Article Defining the process to literature searching in systematic r...
Article Bubble effect: Including internet search engines in systemat...
https://www.dovepress.com/publication-bias-what-is-it-how-do-we-measure-it-how-do-we-avoid-it-peer-reviewed-article-OAJCT
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5953768/
With due respect, Thank you all for the clarifications. The help was really usefull.
Dear Balamurugan Janakiraman
My humble suggestion is not to leave a database that you are preoccupied with the quality of studies. Broader understanding is that most of the papers available in other search engines will also be in Google Scholar. The rationale behind considering multiple search engines is to supplement each other and ensure the exclusivity of evidence in your systematic review. I agree with the concern that some studies with poor quality may find a place in your results, but, such studies may also come from other databases.
So, the issue of quality should be addressed separately using quality assessment or risk of bias tool. Even the quality issue is applicable to Scopus and PubMed also. A bubble effect is applicable to Google Search, not Google scholar. Definitely I agree that it is not an alternative to PubMed, Scopus, WoS, or Embase, etc., but it could be useful that depends on your research question or topic of interest. For serious clinical queries, it is not a good choice but for many topics, it can give a value addition by supplementing your search results.
Article Multidisciplinary Bibliographic Databases
Article Google Scholar to Overshadow Them All? Comparing the Sizes o...
Article Google Scholar
I would exclude the articles that are not good quality. If you look through the references of the most recent articles that come up in your search, you can find further sources that your search may not have found. Actually, I like to do this not just for the most recent articles but for almost all of them, to be comprehensive in my literature review. You may be surprised by how many good articles may have been missed by previously published papers.
I recommend including results from Google Scholar, especially if you want to include gray literature (conference material, non-indexed journals, theses, dissertations, book chapters) or the material you are looking for is very limited, so you need to maximize what you can find. If you download Harzing's Publish or Perish, you can run a Google Scholar search then export results into a table as to record your results in a way that you can later refer back to. You can state in your manuscript that you screened the first 100 results, or whichever number you choose. The caveat here is as you mentioned to avoid low quality material such as papers from predatory journals. You could exclude these outright or utilize a risk of bias / quality rubric for all materials which will help regardless of your search strategy.
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