Suppose we have the following returns for large-company stocks and Treasury bills over a six year period:

Year Large Company US Treasury Bill

1 3.92 5.90

2 14.18 2.53

3 19.37 3.76

4 14.31 7.16

5 31.80 5.42

6 37.08 6.24

Calculate the observed risk premium in each year for the large-company stocks versus the T-bills. What was the standard deviation of the risk premium over this period?

Standard Deviation = ______ %