Perhaps you should try some spelling variations:
ratings risk » patients risk
liang yang » wang yang, yang yang, huang yang
liang ying » liang liying, huang ying, zhang ying
power cost » power costs, power costa, lower cost
risk wrong » risk among, risk along
user cost » user costs
wrong who » wrong why, wrong what, wrong when

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: wang ((liang yang) or (liang ying)) ((user cost) or (power cost)) ratings risk wrong who ;~.
• If you are trying to use Boolean operators, they must be ALL CAPS: wang ((liang yang) OR (liang ying)) ((user cost) OR (power cost)) ratings risk wrong who ;.
• Adding a wildcard symbol may retrieve word variants: wang ((liang yang) or (liang ying)) ((user cost) or (power cost)) ratings risk wrong who ;*.