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

Try widening your search to All Fields.

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• Performing a fuzzy search may retrieve terms with similar spellings: (("improving bank performance series.") or ("improving pupil performance contracts."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving bank performance series.") OR ("improving pupil performance contracts.")).
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