You're right, de la Chapelle is the more relevant condition in this discussion. In general, though, chromosomal abnormalities make lines based on the presence

You're right, de la Chapelle is the more relevant condition in this discussion. In general, though, chromosomal abnormalities make lines based on the presence or absence of particular chromosomes seem arbitrary. I get that you're trying to simplify this by drawing a bright line. I'm sympathetic to that urge. Quick and easy sorting systems are often the most useful approach, even if there are a few false sorts on the margins. But the goal is not always to get as bright a line as possible. Sometimes there are other considerations that are more important, like as GP noted, trying not to bias survey participation. EDIT: Tone.