Perhaps you should try some spelling variations:
"improving past performance series." » "improving past performance studies.", "improving past performance size.", "improving plant performance series.", "improving port performance series.", "improving transit performance series.", "improving fast performance series.", "improving post performance series."
"improve using performance evidence." » "improve business performance evidence.", "improve building performance evidence.", "improve savings performance evidence.", "improve housing performance evidence.", "improved housing performance evidence.", "improve testing performance evidence."

Try widening your search to All Fields.

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

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