Perhaps you should try some spelling variations:
efficiency reduction » efficiency prediction, efficient reduction, deficiency reduction
efficiency education » efficient education, efficiency induction, efficiency mutation
efficiency equation » efficiency evaluation, efficiency situation, efficiency equality

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