Perhaps you should try some spelling variations:
"improving birth performance risk." » "improving firm performance risk.", "improving high performance risk.", "improving port performance risk.", "improving birth performance size.", "improving birth performance based.", "improving birth performance _.", "improving air performance risk.", "improving health performance risk.", "improving growth performance risk."
"improving based performance evidence." » "improving bank performance evidence.", "improving care performance evidence.", "improving board performance evidence.", "improving basic performance evidence.", "improving shared performance evidence.", "improving water performance evidence."

Try widening your search to All Fields.

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

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