# Immersive Tools in Engineering Education--A Systematic Review
## 4 Discussion
### Bias and Systematic Review Limitations  
A critical analysis of bias across all the studies included shows that of all the 31 articles, 11 were rated as high-risk (HR) in at least one domain (bias assessment, bias performance, or reporting bias), the majority of those in performance assessment [20; 24; 25; 38; 39; 40; 42; 44; 45; 49]. These ratings raise concerns about the validity of the findings, since the HR classification was often due to small sample sizes, with nine articles using below 30 participants [21; 23; 24; 26; 29; 31; 40; 43; 48], absence of control groups, or lack of randomization in the sample used, which can undermine the strength and certainty of the conclusions, requiring a cautious interpretation of the outcomes. Small sample sizes increase the risk of bias, the absence of a control group limits the ability to compare obtained results effectively, and the lack of randomization makes it challenging to determine the actual impact of the immersive tools. These limitations are noticeable in several articles in the systematic review. However, these articles were not excluded from the systematic review, as their feedback and knowledge contributions were valuable for developing serious games related to the engineering curriculum. The ROBINS-I tool mainly identified moderate risk (MR) of bias across most domains, although in some cases, specific bias domains were classified as high-risk (HR). Studies assessed using the RoB 2 tool mostly presented low risk (LR) for selection bias, with a few cases classified as MR or HR. The articles assessed with RoB 2 are more reliable and trustworthy due to RoB 2 being designed explicitly for randomized studies, including stricter criteria related to randomization, reducing the risk of bias and increasing credibility. In comparison, studies assessed with ROBINS-I should not be discarded. Still, the evaluation and data assessment should be (and was) performed more carefully due to a high level of bias. To do so, it is vital to critically examine the study designs, sample sizes, and methodologies. As for performance bias, studies and assessments using RoB 2 are classified as LR or MR. On the other hand, studies and assessments using the ROBINS-I tool presented heterogeneity between LR, MR, and HR. Even though some performance bias could exist, the results were always positive, not being strictly affected by the difference in the backgrounds of the samples. Concerning reporting bias, most of the studies were classified as LR and MR, with only a few articles classified as HR using ROBINS-I and RoB 2. This means that the outcomes of the game are trustworthy in both cases, with studies stating what worked and what did not work during the use of the serious game. With these results, even though more than a third of the articles included in this systematic review have at least one domain rated as HR, only one was rated HR in reporting bias. Studies assessed with ROBINS-I were found to have a higher risk of selection and performance bias, which could have influenced the outcome of the results. For RoB 2, the results are more accurate. This can be attributed to the fact that this type of assessment employed distinct methodologies to ensure randomization, thereby amplifying the reliability of the results. Regarding reporting bias, MR remained across both studies, showing that the results presented can be trusted, but still with some caution, which is important to keep a critical perspective. The limitations of this systematic review include the absence of longitudinal studies, the presence of small sample sizes in some of the articles, and the heterogeneity across subjects and samples in different studies. As discussed, the heterogeneity across subjects can impact the articles' performance because of how differently STEM areas work with these immersive tools. There is a lack of consistency in evaluation methods, with studies using diverse criteria and metrics, which makes cross-comparison difficult.