The candidate ratio I’ve seen has been all over the map depending on the company. At one place it was more like 90% of candidates who couldn’t write any code, another place it was closer to 50%, and I’ve worked at some places where nearly every candidate we got was at least somewhat competent as a programmer. The obvious answer is better pre-screening or candidate sourcing, but one of the places with generally high quality candidates was a small startup with no recruiting to pre-screen (although we mainly recruited from local meetups so perhaps that was good sourcing)