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

Try widening your search to All Fields.

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 ("lie groups"))) OR ((("linkage groups") OR ("link groups")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"life groups\") OR (\"lie groups\"))) or (((\"linkage groups\") or (\"link groups\"))))".
• Removing quotes may allow a broader search: (((( life groups ) OR ( lie groups ))) or ((( linkage groups ) or ( link groups )))).
• Adding a wildcard symbol may retrieve word variants: (((("life groups") OR ("lie groups"))) or ((("linkage groups") or ("link groups"))))*.