Perhaps you should try some spelling variations:
"improving end performance review." » "improving end performance risk.", "improving end performance evidence.", "improving und performance review.", "improving esd performance review.", "improving fund performance review.", "improving feed performance review.", "improving e performance review.", "improving eap performance review."
"improving mental performance series." » "improving general performance series.", "improving senegal performance series.", "improving annual performance series.", "improving mental performance studies.", "improving mental performance size.", "improving maternal performance series.", "improving fiscal performance series.", "improving gender performance series."

Try widening your search to All Fields.

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