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

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 effective)) treatments.
• The words AND, OR and NOT may confuse the search; try adding quotes: "7th new workers ((((change effective) OR (change effectively))) or (enhance effective)) treatments".
• Adding a wildcard symbol may retrieve word variants: 7th new workers ((((change effective) OR (change effectively))) or (enhance effective)) treatments*.