# Spam Review Detection Techniques: A Systematic Literature Review
## 2 Systematic Literature Review
### SLR Planning
#### 2.1.3 Review Protocol  
The following part describes the review protocol for performing this SLR. Moreover, it also elaborates the search process, selection of studies, and analysis of data. **Search Process:** Search strings play a significant role in selecting a related set of existing studies. Therefore, the researchers first studied the main concepts and terminology in the spam review detection area and considered different keywords used in the RQs. The researchers tested the alternatives and synonyms for each of the keywords used in the specified RQs. In the end, this study used different Boolean operators ('OR' and 'AND') and wildcard (*) in order to prepare the search string. Table 2 shows the search string, which is joined by AND operator. The population contains different keywords, e.g., \"Spam\" and \"Review\", which are the major keywords that are used to filter out the search records. The search procedure produced 1690 initial studies. Out of these studies, 165 are selected as being relevant and 76 are selected as primary studies. **Selection of Studies:** The selection of primary studies was performed by three types of searches i.e., primary search, secondary search, and snowball tracking. Major research efforts in the domain of spam review detection were started in 2007. Therefore, this study is based on a 12-year duration from 2007 to 2018. This research executed a primary search by using different online research databases (Springer, Elsevier, IEEE, Science Direct, and ACM), conference proceedings, e-journals, and review papers. Researchers of this study used Google and Google Scholar to search the research databases. In the secondary search, the primary search was evaluated by studying the titles, abstracts, and conclusions, and lastly snowball tracking was utilized (i.e., going by the bibliography of works) to \begin{table}
\begin{tabular}{l l l} \hline \hline
**ID** & **Research Question** & **Motivation** \\ \hline \multirow{3}{*}{**RQ1**} & Which feature engineering techniques are used for construction or extraction of features from review datasets? & To understand different available review dataset and approaches of feature engineering and how these approaches help for extraction of useful features from data. \\ \cline{2-3}  & What methods are used to solve the problem of spam review detection? & To identify existing spam review detection models and analyze these models based on their accuracy score. \\ \hline \multirow{3}{*}{**RQ3**} & Which performance metrics are used to evaluate the performance of spam review detection methods? & Study different metrics which are used to evaluate the performance of different spam review detection methods. \\ \cline{2-3}  & & review detection methods. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Research Questions. \begin{table}
\begin{tabular}{l l} \hline \hline
**Population** & **Intervention** \\ \hline \multirow{2}{*}{**(Spam) And (Review)**} & (Spam OR Fake OR Shill OR Opinion Spam OR Spammer OR Social \\  & Spam OR Reviews OR Comments OR Online Comments OR \\ \cline{2-3}  & Detection OR Finding OR Technique OR Method) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Search string. finalize the selected studies. Further, selection of studies using SLR [10; 11] followed automatic and manual search mechanisms to find out the meaningful research available in the respective domain. At first, researchers performed an automatic search, which was based on search strings and is performed in search engines of relevant electronic data repositories. Then, researchers performed a manual search, which was based on studying the title, abstract, conclusion, and snowball tracking. The experimental quality of the selected works is evaluated in the full-text-based analysis that is performed on the remaining 80 research papers. The selection criteria of different papers are dependent upon the raised RQs. The quality of any SLR depends upon the selection of relevant works.