You know what, you’re right. Looks like I’ve gone too long assuming they were interchangeably usable by changing the surrounding words.
I’ll redact my previous statement, though to be clear, I still strongly disagree that one could say that the attackers schizophrenia was definitely a factor in this without having a previously existing mental evaluation and the expertise to understand it. You could say that it’s more likely to have been influenced by his schizophrenia, but as I previously noted, a relatively small minority of schizophrenic people are violent (10-15%).
Letter paper (8.5" x 11" | 215.9mm x 279.4mm) is kinda sorta pretty close to A4 (8.27" x 11.69" | 210mm x 297mm) so without having the two next to each other, it can seem like A4 is just a funny piece of letter, and vice versa. But to answer the actual question, USA and Canada (and apparently the phillipines???) use the “North American Standard” which is a terrifying mess in comparison to the beauty that is the ISO standard.
Edit: typos