Perhaps you should try some spelling variations:
"linkage groups" » "linkage group", "link groups"
"life groups" » "lie groups", "life group", "line groups"
"like groups" » "lie groups", "large groups", "crime groups"
"sink groups" » "using groups", "risk groups", "disk 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 ("like groups"))) OR ((("linkage groups") OR ("sink groups")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"life groups\") OR (\"like groups\"))) or (((\"linkage groups\") or (\"sink groups\"))))".
• Removing quotes may allow a broader search: (((( life groups ) OR ( like groups ))) or ((( linkage groups ) or ( sink groups )))).
• Adding a wildcard symbol may retrieve word variants: (((("life groups") OR ("like groups"))) or ((("linkage groups") or ("sink groups"))))*.