## 4 Experiment 1: Test of Convergent Validity of the Biofeedback System
### Results  
This experiment examines the convergent validity of the used biofeedback system in relation to the Neurosky Mindset measurements and the responses to the state part of the STAI questionnaire.  
The statistical analyses were conducted using SPSS version 20.  
In order to test the concurrent validity of the biofeedback device, we first examined the existence of a significant correlation between:  
1. the biofeedback device measurements regarding galvanic skin response (GSR), heart rate (HR), and skin temperature (SKT) that were received during the training activity while applying the psychometric test.
2. the state part of the State-Trait Anxiety Inventory (STAI) scores (STAISCORE) based on each student's responses, each time s/he was asked to complete this questionnaire during the training phase as part of the psychometric protocol.  
The data used for this evaluation was collected during the training phase, as aforementioned. Thus, the users were connected to the biofeedback device and the Neurosky Mindset while completing the STAI questionnaire at the same time. The biofeedback device provided us with raw galvanic skin response (GSR), skin temperature (SKT), and heart rate (HR) values. From the Neurosky Mindset, we collected anxiety levels and from the STAI questionnaire the corresponding responses. We applied a statistical analysis between these three types of measurements for every student identically at specific time windows (the time period needed for each completion of the state items of the STAI questionnaire during the psychometric protocol procedure). More specifically, we applied [PERSON]'s rank correlation between the STAISCORE variables and the GSR, HR, and SKT biofeedback. The significant moderate correlations found for 12 out of the 15 participants are shown in Table 1.  
Moreover, we examined whether there is any significant correlation between:  
1. The biofeedback device's raw measurements for GSR, heart rate (HR) and skin temperature (SKT) during the training phase, while applying the psychometric test.
2. The Mindset brainwave anxiety measurements during the training phase, while applying the psychometric test. All measurements were collected within the same time period. We used [PERSON]'s Rho correlation between the TRAINLABEL (\(100-\) (Neurosky Mindset anxiety level)) variable and the GSR, HR, and SKT biofeedback. The significant moderate correlations found for 12 out of the 15 participants are presented in Table 2.  
In addition, we examined the correlation between the STAI scores and the values of the aforementioned TRAINLABEL variable during the training phase, while applying the psychometric test for each student. The purpose of this analysis was to discover whether the two valid tools used for the biofeedback system validation and calibration actually measure similar anxiety components. The significant positive correlations found for 12 out of the 15 participants are presented in Table 3.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**User Code** & **Spearman’s Correlation (STAI Scores—Biofeedback Measurements)** \\ \hline  & HR & SKT & GSR \\ \hline User 03 & & \(-\)0.368 ** & 0.248 ** \\ User 04 & & \(-\)0.538 ** & 0.374 ** \\ User 06 & 0.277 ** & \(-\)0.259 ** & 0.234 ** \\ User 07 & 0.361 ** & & 0.550 ** \\ User 08 & 0.362 ** & & 0.369 ** \\ User 09 & 0.221 * & \(-\)0.297 ** & \\ User 10 & 0.496 ** & \(-\)0.202 ** & \\ User 11 & 0.237 * & & 0.521 ** \\ User 13 & 0.351 ** & \(-\)0.281 ** & 0.268 ** \\ User 14 & & & 0.306 ** \\ User 15 & 0.277 ** & \(-\)0.422 ** & 0.604 ** \\ User 16 & 0.497 ** & \(-\)0.381 ** & \\ \hline \hline \end{tabular}  
The resulting significant correlations for 12 (out of the 15) users are moderate or high and support the convergent validity of the used biofeedback device regarding the other two measures of anxiety.