Caption: Dichotomous variables
Text: Discrete variables with only two options, e.g., yes or no, lived or died, male or female.

Exposure to a particular risk factor (e.g., current smoking) could be a dichotomous variable (yes or no).  Prevalent disease status is another example of a dichotomous variable, e.g., classifying each individual as having or not having the disease of interest at a point in time.