## A medical dataset to create graphs

For many of the examples in this book, we will use the following dataset. It gives medical data on 45 people: their names; their gender (a two-level categorical variable); their ethnicity (a four-level categorical variable, labeled 1, 2, and 3); the medical treatment they received (a three-level categorical variable with levels A, B, or C); their age band (a three-level categorical variable with levels Y, M, and E, standing for young, middle-aged, and elderly); their weight (body mass) before treatment (in kg) and weight (body mass) after treatment (in kg), their heights (in cm); whether they smoke (a two-level categorical variable with levels Y and N); whether they perform regular exercise (a two-level categorical variable with levels TRUE and FALSE); and finally, whether or not they recovered after treatment (a two-level categorical variable with levels 1 and 0). We read this dataset as an object called `T`

. The syntax to read this dataset is given in the...