Perhaps you should try some spelling variations:
efficiency validation » efficiency calibration, efficiency evaluation, efficiency calculation
efficiency variation » efficient variation, efficiency fabrication, efficiency evaluation
efficiency taxation » efficient taxation, efficiency equation, efficiency mutation

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: %((efficiency taxation) OR (((efficiency variation) OR (efficiency validation))))%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%((efficiency taxation) or (((efficiency variation) OR (efficiency validation))))%22".
• Adding a wildcard symbol may retrieve word variants: %((efficiency taxation) or (((efficiency variation) OR (efficiency validation))))%22*.