# For 41 cities in the United S

**Question description**

For 41 cities in the United States, the following 7 variables were recorded: Y: Sulphur dioxide content of air in micrograms per cubic meter (SO2) X1: Average annual temperature in degrees F (Temp) X2: Number of manufacturing enterprises employing 20 or more workers (Manuf) X3: Population size in thousands (Pop) X4: Average annual wind speed in miles per hour (Wind) X5: Average annual precipitation in inches (Precip) X6: Average number of days with precipitation per year (Days) This data has been collected to investigate the determinants of air pollution. (a) Look at the correlation matrix of all the explanatory variables. Which two explanatory variables are so highly correlated that they may give cause for concern? (b) Now conduct a regression analysis using all theexplanatory variables. If using StatCrunch store the standardized residuals and the predicted values. Interpret in detail your printout. (c) Examine the residual plots (or construct a residual plot of the standardized residuals and the predicted values if using StatCrunch). What do the plots indicate? (d) Look at the standardized residuals for each city. You will notice from these and your plots that two cities stand out in the model fit as being outliers. Locate these cities and comment. (e) Using the information in the ANOVA table (part b) and the correlation matrix (part a) comment on if any variables should be eliminated from the regression model.

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