Test the hypothesis vs At least one is not . State your conclusion clearly and what it suggests is the preferred model. Examine the residual plots for evidence of model assumption violations. Specify which plots you have looked at and whether there is a problem or not. Examine the leverage values using DotPlot mode in XGobi.
Leverage means how much the observation pulls the fitted surface towards it .
Examine the CooksD. CooksD measures how much the parameter values change when observation is removed from the model. Points that have high CooksD values exert unusually large influence on the fitted model. Examine the plots of VMA vs the independent variables. Mark them with a different color on the Chicago map. State it and interpret the parameter values in the language of the response and independent variables.