Converts a continuous BMI variable into a 4-level factor variable:
Underweight if [-Inf, 18.5), Normal weight if [18.5, 25),
Overweight if [25, 30), and Obese if [30, Inf).
bmi4(x, labels = TRUE)Numeric vector of BMI values.
If TRUE, factor levels are labeled "Underweight",
"Normal weight", "Overweight", and "Obese"; if
FALSE, factor levels are [-Inf, 18.5), [18.5, 25),
[25, 30), and [30, Inf).
Factor variable with 4 levels.