Perhaps you should try some spelling variations:
"improving urban performance series." » "improving urban performance studies.", "improving urban performance size.", "improving bank performance series.", "improving loan performance series.", "improving human performance series."
"improving pupil performance measures." » "improving social performance measures.", "improving model performance measures.", "improving judicial performance measures.", "improving public performance measures.", "improving civil performance measures.", "improving audit performance measures."

Try widening your search to All Fields.

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