Perhaps you should try some spelling variations:
enhance effectiveness » enhancing effectiveness
change effectively » can effectively, challenges effectively, code effectively
change effective » enhance effective, change effects, change effect
new workers » new yorker, new markers, line workers

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: 7th new workers ((((change effective) OR (change effectively))) OR (enhance effectiveness)) treatments.
• Adding a wildcard symbol may retrieve word variants: 7th new workers ((((change effective) or (change effectively))) or (enhance effectiveness)) treatments*.