Perhaps you should try some spelling variations:
"improving social performance series." » "improving school performance series.", "improving fiscal performance series.", "improving financial performance series.", "improving social performance studies.", "improving social performance size."
"improving human performance series." » "improving human performance studies.", "improving human performance size.", "improving loan performance series.", "improving thermal performance series.", "improving chain performance series."

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("improving human performance series.") or ("improving social performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving human performance series.") OR ("improving social performance series.")).
• Removing quotes may allow a broader search: (( improving human performance series. ) or ( improving social performance series. )).
• Adding a wildcard symbol may retrieve word variants: (("improving human performance series.") or ("improving social performance series."))*.