16. Cellphone Customer Retention (k-NN classification). Telecommunications companies providing cell-phone service are interested in customer retention. In particular, identifying customers who are about to churn (cancel their service) is potentially worth millions of dollars if the company can proactively address the reason that customer is considering can-cellation and retain the customer. Data on past customers (some of whom churned and some who did not) has been collected. The variables in this data are listed in the following table.

19. Cellphone Customer Retention (logistic regression). Refer to scenario in Problem 16 regarding the identification of churning cellphone customers. Apply logistic regression using Churn as the target (or response) variable and all the other variables as input variables.

a. Evaluate several candidate models based on their predictive performance on the validation set. Recommend a final model and express the model as a mathematical equation relating the target variable to the input variables. Do the relationships suggested by the model make sense? Try to explain them

b. What is the AUC for the ROC curve for the final model from part (a) on the test set?

Variable Description AccountWeeks number of weeks customer has had active account ContractRenewal 1 if customer recently renewed contract, O if not DataPlan 1 if customer has data plan, O if not DataUsage gigabytes of monthly data usage CustServCalls number of calls into customer service DayMins average daytime minutes per month DayCalls average number of daytime calls Monthly Charge average monthly bill OverageFee largest overage fee in last 12 months RoamMins average number of roaming minutes Churn "Yes" if customer cancelled service, "No" if not Variable Description AccountWeeks number of weeks customer has had active account ContractRenewal 1 if customer recently renewed contract, O if not DataPlan 1 if customer has data plan, O if not DataUsage gigabytes of monthly data usage CustServCalls number of calls into customer service DayMins average daytime minutes per month DayCalls average number of daytime calls Monthly Charge average monthly bill OverageFee largest overage fee in last 12 months RoamMins average number of roaming minutes Churn "Yes" if customer cancelled service, "No" if not