it doesn't logically follow from the fact that you know about a group that there are similar groups.
for example let's say you know a few people who work for the military and they happen to work at Area 51. sure lots of people know military personnel, but your sample is still pretty special. without a good representative sample we simply have no idea.
for example let's say you know a few people who work for the military and they happen to work at Area 51. sure lots of people know military personnel, but your sample is still pretty special. without a good representative sample we simply have no idea.