During Waves IV and V of the Add Health study introduced in Problem Set 1, participants' body mass index (BMI) was calculated as their weight (in kilograms) divided by their squared height (in meters). These BMI measures range between 14.4 and 70.3. A second variable was derived from this, labeled "BMI classification," which distinguishes between six BMI groups: "Underweight (BMI<18.5)" "Normal (18.5BMI<25)" "Overweight (25BMI<30)" "Obese I (30BMI<35)" "Obese II (35BMI<40)" "Obese III (40BMI)" What kind of variable is this "BMI classification" variable