# An Estimation of Speech Privacy Class Based on ISO Parameter
## 4 Results and Discussion
### Correlation between the SPC and SPI Parameters  
A comparative analysis of the \(SPC\) values calculated by (2) and the SPI values calculated by (11) was conducted. The results are shown in Figure 6. All 43 measurement results are presented as black circles, where the \(x\)-coordinate represents the value of the \(SPC\) parameter, and the \(y\)-coordinate represents the value of the \(SPI\) parameter. It can be observed that the measured values are clustered around the hypothetical line \(SPI\) = \(SPC\). This indicates that for the same measurement location, the \(SPC\) and \(SPI\) parameters are approximately the same. However, a more detailed analysis of the relationship between these two parameters is necessary. Based on the values of both parameters, the regression line was determined using the least square deviation criterion. The best-fitted line (solid black line) for the data presented in the diagram is \(y\) = 1.11 \(x\) - 3.17 (\(SPI\) = 1.11 \(SPC\) - 3.17 dB). To evaluate the similarity of the obtained data, Pearson's coefficient of correlation (\(r\)) was calculated, resulting in a value of \(r\) = 0.95. The maximum value of the correlation coefficient (\(r\)) is 1. Comparing these two values, it can be concluded that there is a very good correlation between \(SPI\) and \(SPC\). The \(R\)-squared (\(R^{2}\)) statistical measure, in this case, is 0.91, indicating that the linear regression model describes the analyzed data well. Based on this, it can be stated that the initial hypothesis of a good match between the values of the \(SPC\) parameter and the proposed \(SPI\) parameter is correct. In Figure 6, the red dashed line shows the limits of  
Figure 5: Confidence intervals (95%) at all measurement locations for (**a**) the source room, receiving room, and background noise levels; (**b**) the \(SPC\) parameter. Each point represents a distinct measurement location. the 95% confidence interval for the obtained regression line. In the value range for _SPC_ and _SPI_ below 55 dB, there are only five measurement situations. Also, in the analyzed data, there are only two values higher than 80 dB. Due to the small amount of data in the mentioned ranges, the confidence intervals in those ranges are wider compared to the zone where the majority of analyzed data is located. At the edges of the observed range, the confidence interval values are around \(\pm\)3 dB. On the other hand, the confidence interval values in the middle of the range (around 65 dB) are around \(\pm\)1 dB. Based on the good correlation between the _SPC_ parameter and the proposed _SPI_ parameter, it can be concluded that the evaluation of the state of privacy can also be performed based on the _SPI_ using categories from Table 1. Table 2 provides an overview of the state of speech privacy in the analyzed locations by categories. It is observed that in 25% of the examined cases, the state of speech privacy corresponds to the worst category from the privacy standpoint, i.e., speech from the adjacent room is almost always heard and often understood. In about 30% of locations, speech from the adjacent room is often heard and certain phrases are understood (second and third category). Speech from the adjacent room is unintelligible in only 5% of all locations, and only 11% ensure that speech is essentially unintelligible and rarely heard. None of the 43 analyzed situations can be sorted into the best category (speech imperceptible). Based on the presented results for the values of the _SPC_ and _SPI_ parameters, it is concluded that the state of speech privacy is relatively poor in most of the analyzed situations. When observing the values of the sound partitions' sound reduction index in the observed locations, the insulation conditions mostly seem satisfactory. The mismatch between insulation and speech privacy is a consequence of the low level of ambient noise