# Methods for Noise Event Detection and Assessment of the Sonic Environment by the Harmonic Index
## 3 Results and Discussion
The SEL values for conditioned events are generally lower than those for not conditioned (NC) ones, as reported in Table 1, where median and median absolute deviation (MAD) values are given for the SEL differences conditioned--not conditioned (NC) events across all data. The largest values of MAD (1.4) are observed for the L50 algorithm. Table 1 also gives the p-values obtained by the Wilcoxon test, a non-parametric statistical test to compare two paired groups, reported in bold when there were non-significant differences at the 95% confidence level observed. These non-significant differences were obtained for the L50 and O10 algorithms, as well as for all the algorithms when comparing the SEL values obtained with a time gap \(\tau_{\text{g}}\) of 5 (T5) and 10 (T10) s.  
Considering the labels provided by the ANED procedure at each second of every single event, and the rules to assign the relevant source described in Section 2.2.1, Table 2 reports the percentage of events associated with road traffic noise (RTN), those with sources different from RTN (ANE), mixed events where labels RTN and ANE were present, and the source was assigned, according to the majority of labels of the same type (RTN or ANE), and sources not assigned because of the equal number of labels RTN and ANE in the event (reported as even). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **IRT5** & **IRT10** & **LrT5** & **LrT10** & **L50T5** & **L50T10** & **O10T5** & **O10T10** \\ \hline Median & \(-1.2\) & \(-1.6\) & \(-1.3\) & \(-1.6\) & \(-1.5\) & \(-1.4\) & \(-0.4\) & \(-0.9\) \\ MAD & 0.4 & 0.7 & 0.6 & 0.8 & 1.4 & 1.4 & 0.4 & 0.9 \\ \hline \multicolumn{2}{c}{\(p\) value} & & & & & & & \\ \hline Not conditioned events & & & & & & & & \\ (NC) vs. Conditioned (C) & & & & & & & & \\ T5 vs. T10 & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Differences of SEL values for conditioned (C) minus not conditioned (NC) events detected by the four algorithms; \(p\) values reported in bold correspond to not significant differences at 95% confidence level. Figure 9: Comparison of box plots of SEL for not conditioned (NC) events versus conditioned events detected by the four algorithms. Road traffic noise (RTN) is largely the source producing the events; the percentage of events for which the source is not assigned (even events) is limited to a small value (2-4%). Events that, during their duration, showed both RTN and ANE labels, was about 1/3 of the total. The probability density plots of the number of events detected by each algorithm for both time gaps in each SPL time history, reported in Figure 10, show similar shapes for the time gaps. The sharper distribution and the lowest number of detected events is observed for the algorithm L50, whereas O10 shows the flattest shape. Regarding the duration of the detected events, set to a minimum of 3 s, Figure 11 reports the box plot of the observed durations at each site detected by the IRT5 algorithm. The highest median values (5 s) were observed for the sites Ac on Sunday and Ab on Wednesday in Andorra, and site MI139 in Milan. In all of these sites--road traffic was not the predominant noise source. To get more insight on the relationships among the variables, further analysis was conducted to determine the patterns in the results obtained for the time series; that is the matrix formed by 92 observations and 15 variables, namely the acoustic metrics (\(\mathrm{L_{Aeq}}\), \(\mathrm{L_{A10}}-\mathrm{L_{A90}}\), IR, EVT), the descriptors of the SPL distribution (\(\mathrm{sL_{A}}\) and \(\mathrm{kL_{A}}\)), and the number of events detected by the four algorithms for the two time gaps between events. For this purpose, the principal component analysis (PCA) was performed using the FactoMineR package [34], considering the Euclidean distance between scaled observations (mean = 0, standard deviation = 1). The obtained variable correlation plot is given in Figure 12, where the variable's contribution at the two dimensions is reported on a colored scale.