The way I’ve approached this problem is to classify as first-time mothers all those respondents who gave birth in the last year (fertyr == TRUE), have one child (nchild == 1), and the eldest child’s age is less than or equal to one (eldch <= 1).
My problem is that when I do a sanity check and compare the number of mothers using the method above with a method of classification where I count all mothers who gave birth in the last year and have one child, I get different numbers. Shouldn’t these different classifications yield the same answer? That is, if I know you gave birth in the last year and have one child, isn’t it the case that by definition that child has to be no older than 1?
Thanks in advance.