I often see press releases from non-profits or NGOs talking about "at-risk" youth or groups that are most "at risk" of one horrible thing or another. The thing is, none of them seem consistent as to whether or not the hyphen is supposed to be used, or if it's supposed to be used in one situation, but not another.
I looked up the definition of at-risk (with hyphen), and this is what Oxford Dictionaries Online says:
Adjective Vulnerable, especially to abuse or delinquency:
'a church-run school for the most at-risk children'
Then I looked up at risk (no hyphen) in ODO and this is what it said:
Exposed to harm or danger:
'23 million people in Africa are at risk from starvation'
It looks to me like at-risk is used when immediately preceding the noun that it is describing, like in "at-risk children", while at risk is used when you are using a preposition, like "at risk from starvation" or "at risk of memory loss."
If this is the case, is there any source or style guide that prescribes or explains this phenomenon? After some internet searching, I wasn't able to find anything that documents the usage of hyphens to turn phrases into adjectives.