a positive trendP < 0.0001
Starting from the 0 dB, the first segment (0–14 dB) had a positive trend with significant variability increase ( P < 0.0001), the intermediate segment (14–32 dB) had a negative slope with a significant variability reduction ( P < 0.0001), while the last segment (32–35 dB) had a positive slope with a variability increase ( P < 0.0001).