# Detecting Deceptive Behaviours through Facial Cues from Videos: A Systematic Review
## 3 Materials and Methods  
This section illustrates the methodology for systematically searching and analysing the existing literature on automated face deception detection from videos. The followed methodology was the systematic literature review (SLR) described in the PRISMA recommendations [19] composed of the following steps: (1) identifying the review focus; (2) specifying the review question(s); (3) identifying studies to include in the review; (4) data extraction and study quality appraisal; (5) synthesizing the findings; and (6) reporting the results. The review focus consists of the collection and systematization of the scientific knowledge related to automated deception detection from videos focusing on facial signals. Specifically, we aim to study the methods for video pre-processing, the facial extracted features, the decision-making algorithms, and the available datasets. As required by the second step of the SLR process, the following review questions (RQ) were defined:  
RQ 1: Which methods for video pre-processing are used? ;  
RQ 2: Which facial features for automated deception detection are extracted? ;  
RQ 3: Which decision-making algorithms for automated deception detection are used? ;  
RQ 4: Which datasets for automated deception detection are used? In the third step of the SLR process, the identification of the studies to include in the review was carried out following the four phases of the PRISMA recommendations [19], as shown in Figure 2.  
Figure 2: The PRISMA flow diagram, adapted from [20]. For more information, visit: [[http://www.prisma-statement.org/](http://www.prisma-statement.org/)]([http://www.prisma-statement.org/](http://www.prisma-statement.org/)) (accessed on 9 August 2023). For the identification of an initial set of scientific works, two indexed scientific databases (Web of Science (WoS) and Scopus) containing formally published literature (e.g., journal articles, books, and conference papers) were used. Specifically, WoS and Scopus were used due to their proven usefulness in conducting bibliometric analyses of the existing literature in various research domains to establish trends [21]. Grey literature has not been included in the systematic review because there is no gold standard method for searching grey literature, nor is there a defined methodology for the same, which makes it all the more difficult [22]. The search strings defined to search the scientific papers on the databases are as follows: (\"deeption detection\" OR \"lie detection\" OR \"deceptive behaviour\"' OR \"detect\" deception\" AND \"video\" AND \"facial expression\"\"). Note that this study does not disambiguate among the different forms of deception (e.g., bluff, mystification, propaganda, etc.) because it aims to find studies focused on deceptive behaviours in general without restricting the search to specific forms of deception. During the screening phase, the obtained results were filtered according to the inclusion and exclusion criteria shown in Table 2.  
The full text of the eligible studies was analysed by two reviewers using a quality evaluation checklist composed of four questions and related scores (see Table 3). The \"disagreed\" studies were evaluated by a moderator who provided the final scores.