Application of the bootstrap approach to estimate the confidence interval of the STAR_ICMi index in the Pescara river. The observed index was 0.724, and the 95% confidence interval was 0.699–0.747. The boundary between MODERATE and GOOD class is 0.71. In this example, the river would be classified as GOOD (0.724>0.71), but the confidence interval suggested that the probability of wrong classification was not negligible (in the 16.5% of cases the ecological status would fall into the MODERATE class).