Perhaps you should try some spelling variations:
"The comparison studies" » "The comparison study", "The composition studies"
"The comparison series" » "The comparison string", "The comparison section", "The comparison systems"
"the comparison sites" » "the comparison systems", "the comparison system", "the comparison test"

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: (((("The comparison series") OR ("The comparison studies"))) OR ("the comparison sites")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"The comparison series\") OR (\"The comparison studies\"))) or (\"the comparison sites\"))".
• Removing quotes may allow a broader search: (((( The comparison series ) OR ( The comparison studies ))) or ( the comparison sites )).
• Adding a wildcard symbol may retrieve word variants: (((("The comparison series") OR ("The comparison studies"))) or ("the comparison sites"))*.