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Figure 3: Four parameters, i.e., the average amplitude of the sound and the weighted average frequency (ƒc), standard deviation (ó), and skewness (ã1) of its frequency spectrum, derived from a sound recording in a PVA model are plotted as a function of the degree of bladder outlet obstruction (BOOI). At each value of BOOI, the mean and standard error of the mean of 5 recordings at 12 distances downstream of the obstruction are shown. The critical BOOIvalues are indicated by the dotted lines, unobstructed (Nobs) is defined by BOOI <20 and obstructed (Obs) is defined by BOOI >40 (1, 17). This figure is reproduced from IEEE Transactions on Biomedical Engineering, doi: 10.1109/TBME.2008.919131, © 2008 IEEE. 
