If I have a data set with $n$ patients and I have a categorical variable $X$ for each patient, I want to drop all patients whose $x$ is a particular value.
Question 1: what is the term (preferably the epidemiological term) for variable $X$? (Is it an exclusion criteria variable [I've never seen this term before, I'm just guessing], or is there a commonly used term?)
Next, I want to subset the resulting data set into two data sets according to the values of a dichotomous variable $Y$ for each patient such that all patients for which $y = 0$ will go in data set A whereas all patients for which $y = 1$ will go in data set B. I will then treat data sets A and B separately and do statistical tests within each. Following this, I would perform comparisons between A and B.
Question 2: what is the term (again preferably the epidemiological term) for variable $Y$? (I was thinking something along the lines of subsetting variable, but again, I've never seen this term.)