Perhaps you should try some spelling variations:
"improving maternal performance metrics." » "improving national performance metrics.", "improving thermal performance metrics.", "improving lanterns performance metrics.", "improving maternal performance contracts.", "improving maternal performance measures.", "improving maternal performance contract.", "improve maternal performance metrics.", "improving water performance metrics."
"improving human performance risk." » "improving loan performance risk.", "improving thermal performance risk.", "improving company performance risk.", "improving human performance size.", "improving human performance based.", "improving human performance _.", "improving urban performance risk.", "improving rural performance risk."

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving human performance risk.") OR ("improving maternal performance metrics."))~.
• Removing quotes may allow a broader search: (( improving human performance risk. ) or ( improving maternal performance metrics. ))~.
• Adding a wildcard symbol may retrieve word variants: (("improving human performance risk.") or ("improving maternal performance metrics."))*.