There are endless difficulties in definitions. Here's an excellent example.
The USA is undertaking research into crime against and within ethnic racial groups. It is trying hard to define groups. Here's a quote: " If issuing specific guidelines for the collection of detailed White race and ethnicity data, should OMB adopt the NCT format, which includes separately German, Irish, English, Italian, Polish, and French?"
It's not the fault of the US Government that it's confused. We, the English, have the most tangled ethnicity imaginable. The only effective classification for us is "unclassifiable."
