Correct: either one category (T for total), or three/four categories (M for male, F for Female, U for unknown and T for total, where M+F+U=T). In some databases M and F (and U) are given, but no T, in others T is sometimes used where U is more appropriate.
Correct: either one category (T for total), or three/four categories (M for male, F for Female, U for unknown and T for total, where M+F+U=T). In some databases M and F (and U) are given, but no T, in others T is sometimes used where U is more appropriate.