Before revision:  The investigations have been carried out for both long (~18 years) and shorter  (~9 years) terms that include the dot-com bubble and the 2008 crash periods . In all cases, a linear fit can be obtained for the risk and excess return profiles , both for long and shorter periods.
After revision:  The investigations have been carried out for both long (~18 years) and shorter (~9 years) terms that include the dot-com bubble and the 2008 crash periods , show that a linear fit can be obtained for the risk and excess return profiles , both for long and shorter periods.