Perhaps you should try some spelling variations:
"improving national performance series." » "improving regional performance series.", "improving operational performance series.", "improving educational performance series.", "improving maternal performance series.", "improving natural performance series.", "improve national performance series.", "improving national performance studies.", "improving national performance size."
"improving rural performance metrics." » "improving rural performance measures.", "improving euract performance metrics.", "improving larval performance metrics.", "improving pupil performance metrics."

Try widening your search to All Fields.

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• Performing a fuzzy search may retrieve terms with similar spellings: (("improving rural performance metrics.") or ("improving national performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving rural performance metrics.") OR ("improving national performance series.")).
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• Adding a wildcard symbol may retrieve word variants: (("improving rural performance metrics.") or ("improving national performance series."))*.