18. Has the number of home runs hit by Major League teams been changing over time? For 51 years, from 1960 to 2010, the average number of home runs hit per game per team for each season was computed to assess any change over time. Initially, simple linear regression was used to study the trend in home runs hit over the period 1960 to 2010, by using year to predict the average number of home runs per game per team in that year. However, it was pointed out that after the 1976 season the manufacturer of Major League baseballs was changed from Spalding to Rawlings. Because the change in the baseball used might affect the number of home runs (for example, if Rawlings produces a livelier ball, this would likely lead to more home runs), it was decided to include an additional variable, namely l0. If before l9?6 [that Ii. the Spalding baseball was used) .'vlauufacturet : ' I'l. if after 1976 (that is- the Rawlings baseball was used) A multiple regression analysis was performed using the model ElAvg. home runs per game per team = b0+ b1(Year) + b2(Manufacturer) The following results were obtained. Analysis of Variance Source df Sum of squares Model 2 0.744384 Error 48 2.53933 Parameter Estimates Variable df Parameter estimate Standard error Intercept 1 -27.9118 12 .89 Year 1 0.014977 0.0065 Manufacturer 1 -0. 107816 0.11573 What proportion of the variability in the response variable is explained by this model?r A) 5.1% B) 22.7% C) 27.2% D) 74.4%