2.2.2. Conduct a Comprehensive Literature Search

The next step was to conduct a comprehensive literature search in order to identify relevant studies. This should include using a combination of database-specific keywords and subject headings, and the search should be guided by inclusion and exclusion criteria based on the research questions.

The inclusion criteria for this study were as follows: (1) research design: randomized controlled trials (RCTs) or quasi-experimental research; (2) treatment program: biofeedback interventions alone or biofeedback combined with other techniques; (3) duration of training: interventions with a minimum duration of three weeks; (4) population type: patients, students, women, or workers; and (5) specific clinical symptoms: stress, anxiety, and depression. The exclusion criteria for this study were as follows: (1) studies that were not clinical, e.g., descriptive and case studies; (2) those that used non-biofeedback intervention; and (3) those where the sample size was less than twenty.

The search was limited to articles published in English. Following the initial search, duplicates were removed, and the remaining studies were screened based on titles and abstracts. Full-text articles were then assessed for eligibility based on the predefined inclusion and exclusion criteria. The reference lists of selected articles were also reviewed for additional relevant studies. The final set of studies meeting the inclusion criteria were included in the analysis, and their findings were synthesized in order to address the research questions, as shown in Fig. (​(22).

PRISMA flow diagram adapted to examine included studies.