## 4 Experimental Results
### Statistical Results
\begin{table}
\begin{tabular}{l c c c c c c c c c c c} \hline \hline
**mmHg** & **ANN** & \multicolumn{3}{c}{**MLR**} & \multicolumn{3}{c}{**SVM**} & \multicolumn{3}{c}{**LSTM**} & \multicolumn{3}{c}{**GP**} & \multicolumn{3}{c}{**GFSDP**} \\  & **SBP** & **DBP** & **SBP** & **DBP** & **SBP** & **DBP** & **SBP** & **DBP** & **SBP** & **DBP** \\ \hline ME & 0.17 & 0.27 & 0.57 & \(-\)2.81 & 0.46 & \(-\)2.59 & \(-\)1.29 & \(-\)1.46 & 0.10 & 0.10 & 0.08 & 0.15 \\ SDE & 15.68 & 12.75 & 15.93 & 11.21 & 14.70 & 10.96 & 14.22 & 9.87 & 13.30 & 9.28 & 10.83 & 8.31 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: ME and SDE relative to the reference ABP and the conventional ANN, MLR, SVM, LSTM, GP algorithms and using the proposed GFSDP algorithm. plots (Figure 5c,d). The limits of agreement (bold horizontal lines in Figure 5) used in this study were (ME \(\pm\) 2 \(\times\) SD) for all plots. The bias (horizontal center lines) for all plots was small (\(\leq\)\(\pm\)0.5 mmHg). These results indicate that the cuffless BP estimates obtained by the proposed GFSDP algorithm and conventional SVM were in close quantitative agreement with those obtained by the ABP reference values without being overly biased in any direction. The CIs represent the uncertainties from the GFSDP when estimating cuffless BP. Table 10 shows the lower and upper CI estimations obtained using the GFSDP algorithm. The CIs for the SBP and DBP obtained using the GFSDP with bootstrap algorithm GFSDPBT were smaller than those obtained using conventional methods. The difference between 10.19 mmHg and 11.55 mmHg of the GFSDP and GP algorithm for the SBP and DBP was confirmed. The results of the CI estimation were also shown by applying the Student's t-distribution to the conventional algorithms. The proposed GFSDP algorithm exhibited a slight performance loss compared with the BHS protocol [46], as shown in Table 8. The MAEs were 49.49% (\(\leq\)5 mmHg), 73.01% (\(\leq\)10 mmHg), and 84.97% (\(\leq\)15 mmHg) for the SBP and 60.26% (\(\leq\)5 mmHg), 85.39% (\(\leq\)10 mmHg), and 93.74% (\(\leq\)15 mmHg) for the DBP, as shown in Table 8. Therefore, the proposed GFSDP obtained classes C and B for evaluating SBP and DBP. Furthermore, the proposed GFSDP algorithm was more accurate than conventional algorithms for cuffless BP estimation. The SDE of the ME was also evaluated according to the AAMI protocol [47]. The proposed GFSDP algorithm for the SBP (10.83 mmHg) and DBP (8.31 mmHg) had a lower SDE of the ME than conventional algorithms; however, all algorithms failed to meet the AAMI criteria, as shown in Table 9. Thus, the AAMI standards are stringent. Figure 5 shows the SDE results of the ME of the proposed GFSDP and SVM algorithms. These results indicate that the results of the SVM were slightly more spread out than those of the proposed algorithm. This further proves the superiority of the proposed algorithm, in addition to its low MAE. Moreover, the proposed GFSDP algorithm is more favorable because it correctly estimated errors based on the weighted feature subset. Therefore, the GFSDP process accurately estimated cuffless BP values. Cuffless BP-measuring devices typically provide single-point predictions without CIs. Therefore, predicting CIs for cuffless BP measurements improves reliability. Thus, this study predicted CIs using the GP and GFSDP algorithms to express uncertainties in cuffless BP estimation. This study extracted four to eight PPG segment waveforms from each patient's record. A small sample size of each patient affected the accuracy of the bootstrap CI estimation. The results confirmed that the CIs obtained from the proposed GFSDP\({}_{\text{BT}}\) for SBP and DBP were also wide. The CIs derived from the conventional algorithm using the Student's t-distribution (ST) were broader than those obtained from the proposed method for both SBP and DBP, as shown in Table 10. The CI estimates based on the ST distribution are adequate when the sample size from each patient is large (at least 30) [8].