Perhaps you should try some spelling variations:
enhance effective » enhancing effective, enhance effectiveness, distance effective
change effective » change effectively, change effects, change executive
change effect » change effects, changes effect, charge effects
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 effect))) OR (((change effective) OR (change effect))ly))) OR (enhance effective)) treatments.
• The words AND, OR and NOT may confuse the search; try adding quotes: "7th new workers ((((((change effective) OR (change effect))) or (((change effective) OR (change effect))ly))) or (enhance effective)) treatments".
• Adding a wildcard symbol may retrieve word variants: 7th new workers ((((((change effective) OR (change effect))) or (((change effective) OR (change effect))ly))) or (enhance effective)) treatments*.