I'm looking for a less clunky way of saying "a group of which I'm not a part" or "a group to I don't belong." I would prefer a one-word adjective, so that I could talk about "________ groups."
So far, the closest word to what I'm looking for seems to be outlying:
Far away from the center of a place; remote from a center or main body. (Merriam-Webster)
This would fit the fact that the group is figuratively far away from me because I'm not a part of it, but I hesitate to use it because it also seems to imply that the group is an outlier from the norm, an extreme or "fringe" group. This connotation is supported by Dictionary.com's secondary definition:
Lying at a distance from the center or the main body; remote; out-of-the way
Lying outside the boundary or limit
Is there a better adjective than outlying to describe any group, whether mainstream or fringe, to which I don't belong?
EDIT: Here is the context that I would put the word in.
Studies have shown that people are more likely to be suspicious of members of __________ groups and attribute negative qualities to them while overlooking the same qualities in members of their own group.