Snowballing in Systematic Reviews

Last weekend we had a short trip to Bhimtal, a small hill station in Uttarakhand near Nainital.  To distract myself from early morning boredom in the train, I took out a book from my bag. It was an interesting book by Ruskin Bond by the title “Adventures in Reading”, and it was indeed a pleasure reading. In this book Mr. Ruskin Bond wrote about Mr. Turner who was an 18th century English romantic painter who mostly painted sunsets and shipwrecks. Being an amateur artist, I was interested in finding out more about Mr. Turner. When I returned from my journey, I Googled about Mr. Turner. I was glad to find an autobiography movie on Turner by the name of “Mr. Turner” available on Amazon prime videos. When I browsed Amazon prime videos looking for the movie, I found there some more interesting movies related to other artists. I really enjoyed watching Mr. Turner.  An artificial intelligence enabled feature in prime video recommends you more videos based on the videos you have searched earlier.

Fig: View of Sattal from the hills of Bhimtal

Fig: View of Sattal from the hills of Bhimtal

This is similar to how snowballing method of searching new studies works in systematic reviews. We search for some relevant studies using common Internet browsers using some general search terms. Now from these studies we get more references for other studies.  And then from these studies you get more new references. This is basically pursuing references of references and known as the method of snowballing used to find literature in systematic reviews.(Greenhalgh & Peacock, 2005) Snowballing involves tracking of references by scanning the reference lists of all full text papers and then based on the judgment of reviewer it can be decided whether to pursue these further or not. This is an established method and being very commonly used in literature searches across different disciplines.(Wohlin, 2014) This helps in finding references, new search terms and also information on new database, journals and websites for further searches. This can also help finding prominent researchers working in that field. Authors often specialize in their field, and they cite their work. I was once conducting a review of literature on how equity can be assessed through systematic reviews, and I have found that most of these studies were led by Dr Vivian Welch who is currently the CEO of the Campbell Collaboration. As far as the efficiency and sensitivity of searches conducted through snowballing is concerned it is found that snowballing is comparable to database searches provided, we had a suitable start set. (Badampudi et al., 2015)

A good search strategy plays a key role in a successful systematic literature study. Traditionally, database searches have been the common practice, which is now being complemented with many new methods like snowball searches and searches based on machine learning and artificial intelligence. Combining these approaches can help generate a comprehensive search result.

Found on Amazon Prime videos my next movie on the watch list is “Loving Vincent”. It’s a story depicted in oil painted animations about famous Dutch artist Vincent Willem van Gogh.


Badampudi, D., Wohlin, C., & Petersen, K. (2015). Experiences from using snowballing and database searches in systematic literature studies. ACM International Conference Proceeding Series27-29-April-2015. https://doi.org/10.1145/2745802.2745818

Greenhalgh, T., & Peacock, R. (2005). Effectiveness and efficiency of search methods in systematic reviews of complex evidence: audit of primary sources. BMJ331(7524), 1064–1065. https://doi.org/10.1136/BMJ.38636.593461.68

Wohlin, C. (2014). Guidelines for Snowballing in Systematic Literature Studies and a Replication in Software Engineering. https://doi.org/10.1145/2601248.2601268

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