Perhaps you should try some spelling variations:
"improving human performance reviews." » "improving human performance review.", "improving human performance reports.", "improving human performance risks.", "improving loan performance reviews.", "improving thermal performance reviews.", "improving chain performance reviews."
"improving firm performance series." » "improving firm performance studies.", "improving firm performance size.", "improving firms performance series.", "improving air performance series.", "improving erm 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 reviews.") or ("improving firm performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving human performance reviews.") OR ("improving firm performance series.")).
• Removing quotes may allow a broader search: (( improving human performance reviews. ) or ( improving firm performance series. )).
• Adding a wildcard symbol may retrieve word variants: (("improving human performance reviews.") or ("improving firm performance series."))*.