Perhaps you should try some spelling variations:
"improving overall performance series." » "improving average performance series.", "improving thermal performance series.", "improving governance performance series.", "improving overall performance studies.", "improving overall performance size.", "improving coverage performance series.", "improving rural performance series.", "improving federal performance series."
"improving social performance metrics." » "improving social performance measures.", "improving school performance metrics.", "improving fiscal performance metrics.", "improving financial performance metrics."

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