Perhaps you should try some spelling variations:
"improving central performance metrics." » "improving control performance metrics.", "improving general performance metrics.", "improving contract performance metrics.", "improving central performance measures.", "improving mental performance metrics.", "improving federal performance metrics.", "improving neural performance metrics."
"improving basic performance series." » "improving basic performance studies.", "improving basic performance size.", "improving based performance series.", "improving music performance series.", "improving baseline performance series.", "improving air performance series.", "improve basic 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 central performance metrics.") or ("improving basic performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving central performance metrics.") OR ("improving basic performance series.")).
• Removing quotes may allow a broader search: (( improving central performance metrics. ) or ( improving basic performance series. )).
• Adding a wildcard symbol may retrieve word variants: (("improving central performance metrics.") or ("improving basic performance series."))*.