# What's a clear explanation of “Shared environment”?

I often come across the term "Shared environment" (as opposed to "Non-shared environment"). I think I understand non-shared environment, but shared environment is very confusing to me.

Can someone give a good explanation with examples please? Especially in regards to how can shared environment contribute to any difference at all in explaining variance?

I know the claim is that it explains very little, i.e. most of the variance due to environment is due to non-shared. But how is even a small variance due to shared environment possible? I mean, if two people (or siblings) went to different schools, and their income outcome was different, you could talk about the non-shared environment (school) that was different between them. But if they went to the same school, how can this shared environment contribute to any difference at all, even if very little.

• Can you give an example reference of one of the places you see these terms? It would be easier to give an explanation based on the specific situation you have in mind. I have a guess but don't want to write up the answer if it's something else that has you confused :) – Bryan Krause Nov 8 '19 at 0:27
• Hi Bryan, I've come across this terminology in several papers/discussions on the impact of genes and environment. Often the theme is that shared environment is not important. media.springernature.com/lw685/springer-static/image/… – get_going Nov 8 '19 at 1:36
• @BryanKrause, you'll also see charts or pie diagrams showing three items: genes (large %), non-shared env (also large %), shared env (small %). The first two make sense, I think: Different genes explain difference in outcomes, ok. Different environments explain difference in outcomes, ok. But how can shared/same environment explain difference in outcomes? Even if it explains a small difference - how can the same environment explain any difference at all? – get_going Nov 8 '19 at 2:03