13.23. For the Crime2 data file at the text website, let z be a dummy variable for whether a state is in the South, with z = 1 for AL, AR, FL, GA, KY, LA, MD, MS, NC, OK, SC, TN, TX,VA, WV.

(a) Not including the observation forD.C., analyze the relationship between y = violent crime rate and z, both ignoring and controlling for x = poverty rate. Summarize results.

(b) Repeat the analysis with D.C. in the data set, setting z = 1 for it. Is this observation influential? Summarize results.