What I read about was an answer to the question "how much can you explain with genes", i.e. not 80% of cases are explained completely by genes, but genes account for 80% of the variation. It's what's called heritability in psychology. Most or all cases are best explained by a combination of genetic and environmental factors. And also, even though 80% of the variation (hope I got it correct this time) could possibly, assuming that number is correct, be explained by genes, that doesn't mean that environmental factors aren't more important. It could be that all cases of schizophrenia could be prevented by changing the environment for those who are at risk. So it's not a static number. Heritability is a difficult concept and I doubt I did it justice in this paragraph so feel free to correct me. It's been a while since I read about heritability so I reckon some of what I've written here might be incorrect.