6. The following data in Table 4.11 was collected from a study of the effect of stream characteristics on fish biomass. The regressor variables are x1: Average depth of 50 cells x2: Area of stream cover (i.e., undercut banks, logs, boulders, etc.) x3: Percent of canopy cover (average of 12) x4: Area ≥ 25cm in depth The response variable is y, the fish biomass. The data set is as follows:

Table 4.11 Fish Biomass Data Observation y x1 x2 x3 x4 1 100 14.3 15.0 12.2 48.0 2 388 19.1 29.4 26.0 152.2 3 755 54.6 58.0 24.2 469.7 4 1288 28.8 42.6 26.1 485.9 5 230 16.1 15.9 31.6 87.6 6 0.0 10.0 56.4 23.3 6.9 7 551 28.5 95.1 13.0 192.9 8 345 13.8 60.6 7.5 105.8 9 0.0 10.7 35.2 40.3 0.0 10 348 25.9 52.0 40.3 116.6 Data Source: Raymond H. Myers: Classical and Modern Regression With Application, p.