Answer: Zero
Step-by-step explanation:
The Correlation Coefficient measures the relationship between 2 variables under study and ranges from -1 to +1 which -1 meaning that the two are perfectly negatively correlated and +1 meaning they are perfectly positively correlation. A Correlation Coefficient of 0 means that there is no relationship.
An efficient market is one where all information is available to every market participant. This means that one cannot use information from one period to make abnormal profits in another period because all information is available. The Correlation Coefficient will therefore show 0 because information from the previous period is not being used in another period meaning there is no relationship between stock returns.