Categorical variable

(a) In the use of a categorical variable with n possible values, explain the following:    1. Why only n – 1 binary variables are necessary    2. Why using n variables would be problematic(b) Describe how logistic regression can be used as a classifier.(c) Discuss how the ROC curve can be used to determine an appropriate threshold value for a classifier(d) If the probability of an event occurring is 0.4, then    1. What is the odds ratio?    2. What is the log odds ratio?