# Mobile Learning and Its Effect on Learning Outcomes and Critical Thinking: A Systematic Review
## 3 Materials and Methods
### Document Selection and Search Approach  
A search was conducted on 1 May 2024 in the Web of Science (WoS). This database's selection was explained by its wide international recognition for including prestigious journals in different areas of knowledge and for its extensive coverage [36]. Moreover, as a selective, structured and balanced database, its use facilitates a variety of informative purposes [37] and ensures a consistent comparison of studies within a sound methodological framework.  
A search protocol was delineated for the database that included the definition of key descriptors, inclusion and exclusion criteria for all relevant papers, and methods for retrieval and evaluation of articles. The descriptors used were: \"mobile learning\" or \"m-learning\" (All fields). The search was also guided by the definition that the concepts of \"higher education\" or \"university\" should be found in the abstract. The inclusion criteria are defined as follows:  
* Type of Document: Articles as they are the primary means of scientific communication.
* WoS Index: Social Sciences Citation Index (SSC), Science Citation Index-Expanded (SCI-E), and Arts & Humanities Citation Index (A&HCI). Emerging Sources Citation Index (ESCI) is excluded as it mainly incorporates journals of regional importance [38].
* Language: English is recognized as the language of international science, and continues to dominate scientific activities to this day [39].
* Time period: 2015-2024. The reason for this is because m-learning is a field that is continuously and rapidly evolving, and findings from older work may no longer be applicable today. This ensures the relevance and currency of our research [5].
* Study type and participants: Empirical (primary/participatory) research focusing on undergraduate students.
* Context: Research should not have been conducted during the COVID-19 pandemic since, in general, the use of technologies in teaching was mandatory and sudden for remote course delivery [40; 41], which may have consequences for design, acceptance by students, and evaluation of the real effects (this condition does not apply to distance education universities).
* Concerning RQ1, studies that objectively measure the achievement of learning outcomes are included (self-perceived achievements are excluded). As an inclusion criterion, it is also defined that those studies with experimental or quasi-experimental designs must have a control group (same cohort) to measure the real effects of m-learning initiatives.
* Concerning RQ2, studies that objectively (e.g., test) and subjectively (opinion, self-reflection, and others) measure changes in the levels of critical thinking are included.  
Figure 1 shows the steps involved in selecting the sample. The initial search identified a total of 1980 papers. However, this number was reduced to 399 when the WoS filters were applied according to the defined inclusion/exclusion criteria (type of document, index, language, and year of publication). During the second stage, the abstracts of all these papers were read, and 122 moved on to the stage that involved reading the full papers to assess their eligibility. Finally, the sample consisted of 50 articles.  
It is important to note that the selection process was carried out in two phases. In the first phase, the team members conducted an independent reading of the articles to minimize possible biases. Then, continuous communication was maintained among all team members to ensure a solid consensus on the inclusion of each article in the analysis.