This repository includes the data of a Randomized Controlled Trial (RCT) that was reported on in the article titled "A Randomized Controlled Trial Assessing the Efficacy of a Virtual Reality Biofeedback Video Game: Anxiety Outcomes and Appraisal Processes" by Weerdmeester and colleagues (2020). The study assessed the efficacy of a virtual reality biofeedback video game (DEEP) in reducing anxiety symptoms. In addition, engagement and cognitive appraisals including self-efficacy, locus of control, and threat-challenge were explored as potential mechanisms of change. Undergraduates with elevated anxiety symptoms (N = 112) were randomly assigned to four training sessions in the lab with either DEEP, a biofeedback video game, or a smartphone-guided breathing application. Trait anxiety was measured at screening (two weeks prior to the training), pre-test, post-test, and three months later. State anxiety was assessed before and after each individual training session. Engagement as well as all cognitive appraisals were assessed after each training session.This repository includes the following files:- A word file which describes the complete method and procedure of the corresponding Randomized Controlled Trial study, including a description of how the data was analysed.- Two data-sets(one in .sav and one in .CSV format) with all the data that was reported on in the corresponding article, includingraw data of participant characteristics and single-item questions as well as the sum-scores, ratio-scores or difference scores of the main outcomes.- A data codebook (in .xlsx format) including a description of of the variables in the data-set including the labels, values and the scales of the corresponding questionnaire items.Information regarding missing values:Missing values on the variables 'gamehrswk' and 'gamehrswknd' are the result of these questions being skipped because participants answered 'No' on a previous question asking whether or not they play video games (variable 'doyougame').Missingness on other values was due to participants dropping out of the training or not filling out the online follow-up questionnaire. Information about the extent of and reasons for attrition are included in Figure 1, which is included in DEEP_RCT_Data_Method_Procedure.docx. The method section in this document also describes how missingness was dealt with in the analyses.