## 4 Results
### Physiological Data Analysis  
As shown in Figure 4 and Table 2, we collected HRV data from two experimental stages and plotted them on the same chart. We measured and recorded heart rate (HR) signals using a proven photoplethysmogram (PPG) sensor (MDL0025, 3.3 V, 10 mA) [56] attached to the child's index finger. The HR signals are then transmitted to the system and processed to derive Inter-Beat Interval (IBI) and Heart Rate Variability (HRV) data. Root Mean Square of Successive Differences (RMSSD) is a statistical measure used in HRV analysis and as the HRV parameter for its widespread use in short-term stress assessment [57]. Lower RMSSD values indicate higher stress levels. The RMSSD values for each participant, along with their baseline RMSSD (BaseRMSSD), were recorded in a TXT file in chronological order.  
For later comparison, the RMSSD data were kept in their original sequence, with duplicate, outlier, and zero values removed, retaining only the unique BaseRMSSD. The chart shows significant variations in RMSSD changes across different participants, with considerable individual differences. Some children (e.g., C16, C18, and C22) exhibited lower stress levels in both stages and showed further reduction in stress over time. In contrast, some children (e.g., C7) remained in a higher stress state throughout the experiment. We performed a t-test on HRV data from Stage 1 and Stage 2 (mean value per stage and dynamic data) to compare differences. The Shapiro-Wilk test was used to assess whether the data followed a normal distribution. The result showed a \(p\)-value less than 0.05, indicating that  
\begin{table}
\begin{tabular}{c c c} \hline
**BaseRMSSD (M \(\pm\) SD)** & **Stage 1 RMSSD (M \(\pm\) SD)** & **Stage 2 RMSSD (M \(\pm\) SD)** \\ \hline
51.97 \(\pm\) 20.4 & 56.62 \(\pm\) 29.96 & 57.24 \(\pm\) 26.73 \\ \hline \end{tabular}
\end{table}
Table 2: Statistics of HRV data, including mean value and standard deviation.  
Figure 4: HRV data at two stages for all children.  
the data significantly deviated from normal distribution. Then, the Wilcoxon signed-rank test was applied. The result yielded a \(p\)-value of 0.4799 (>0.05), suggesting that the RMSSD difference before and after the introduction of the encouragement prompt system was not significant. We also conducted a non-parametric method (Mann-Whitney U test) to statistically analyze the differences in stage means. The result yielded a \(p\)-value of 0.5384 (>0.05), suggesting the encourage prompt for parents did not cause a significant change in children's RMSSD. Therefore, Hypothesis 2 is rejected, as there is no significant stress relief at the physiological level. The means and median RMSSD values for Stage 2 were slightly higher than those in Stage 1, with most participants showing a slight upward trend in RMSSD during the experiment. Compared to Stage 1, Stage 2 RMSSD data were more concentrated and stable.  
Additionally, the feedback device itself may have induced a placebo effect, leading children to feel \"helped\" or \"the device can help them,\" which could have contributed to relaxation and a subsequent increase in HRV. Parental verbal or emotional support, combined with the information feedback from the device, might have provided dual feedback--both behavioral and physiological--helping children regulate themselves and maintain higher HRV.