Perhaps you should try some spelling variations:
"improving worker performance series." » "improving worker performance studies.", "improving worker performance size.", "improving work performance series.", "improving market performance series.", "improving poor performance series.", "improving water performance series."
"improving co performance measures." » "improving ceo performance measures.", "improving do performance measures.", "improving core performance measures.", "improving eco performance measures.", "improving crop performance measures.", "improving ict performance measures."

You may be able to get more results by adjusting your search query.

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