Perhaps you should try some spelling variations:
"improving voluntary performance review." » "improving country performance review.", "improving entry performance review.", "improving industry performance review.", "improving voluntary performance risk.", "improving voluntary performance evidence."
"improving local performance series." » "improving local performance studies.", "improving local performance size.", "improving social performance series.", "improving global performance series.", "improving total performance series.", "improving fiscal performance series."

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: (("improving local performance series.") OR ("improving voluntary performance review."))~.
• Removing quotes may allow a broader search: (( improving local performance series. ) or ( improving voluntary performance review. ))~.
• Adding a wildcard symbol may retrieve word variants: (("improving local performance series.") or ("improving voluntary performance review."))*.