Perhaps you should try some spelling variations:
"linkage groups" » "linkage group"
"life groups" » "lie groups", "life group", "line groups"
"like groups" » "lie groups", "large groups", "crime groups"
"link groups" » "sink groups", "disk groups", "linear groups"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("life groups") OR ("like groups"))) OR ((((("linkage groups") OR ("link groups"))) OR ("risk groups"))))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"life groups\") OR (\"like groups\"))) or (((((\"linkage groups\") or (\"link groups\"))) or (\"risk groups\"))))*".
• Removing quotes may allow a broader search: (((( life groups ) OR ( like groups ))) or ((((( linkage groups ) or ( link groups ))) or ( risk groups ))))*.