Perhaps you should try some spelling variations:
"improving voluntary performance risk." » "improving country performance risk.", "improving entry performance risk.", "improving budgetary performance risk.", "improving voluntary performance size.", "improving voluntary performance based.", "improving voluntary performance _."
"improving key performance series." » "improving key performance metrics.", "improving key performance reviews.", "improving key performance review.", "improving _ performance series.", "improving market performance series.", "improving firm performance series.", "improving beef performance series.", "improving city performance series.", "improving feed 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 voluntary performance risk.") or ("improving key performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving voluntary performance risk.") OR ("improving key performance series.")).
• Removing quotes may allow a broader search: (( improving voluntary performance risk. ) or ( improving key performance series. )).
• Adding a wildcard symbol may retrieve word variants: (("improving voluntary performance risk.") or ("improving key performance series."))*.