The efficiency of a stock market is principally measured by its information efficiency and functionality efficiency.Both metrics are closely related to the information of stock markets.However,there is no uniform definition of information in the economy field since researchers may have various opinions on the information of stock markets.In this research,a comparatively strict definition of information in sense of economy is presented.Based on this definition,the optimal conditions to reach the maximum information efficiency and functionality efficiency of stock markets are derived.The conclusion is,only when the market's operation and information transmission mechanisms are fully effective,its information completeness degree is optimal,all investors take optimal equilibrium actions,and the information efficiency and functionality efficiency of stock markets will be optimal.Based on the conclusions,the information efficiency and functionality efficiency of reality stock markets in China are studied and the corresponding supervision countermeasures are suggested.
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