Perhaps you should try some spelling variations:
"improving country performance series." » "improving country performance studies.", "improving country performance size.", "improving voluntary performance series.", "importing country performance series.", "improving community performance series."
"improving sector performance series." » "improving sector performance studies.", "improving sector performance size.", "improve sector performance series.", "improving eco performance series.", "improving sewer performance series."

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("improving country performance series.") OR ("improving sector performance series."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"improving country performance series.\") OR (\"improving sector performance series.\"))".
• Removing quotes may allow a broader search: (( improving country performance series. ) OR ( improving sector performance series. )).
• Adding a wildcard symbol may retrieve word variants: (("improving country performance series.") OR ("improving sector performance series."))*.