9
3 Risk
Choosing the factors • All factors must be a priori factors. That is, even though
the factor returns are uncertain, the factor exposures must be known a priori, i.e., at the beginning of the period. Three types of actors:
actively
5
3 Risk
Defining risk
• Variance will add across time if the returns in one interval are uncorrelated with the returns in other intervals of time. The autocorrelation is close to zero for most assets. Thus, variances will grow with the length of the forecast horizon and the risk will grow with the square root of the forecast horizon.
• Over 80% people think they are smart than market
• For smart managers, they have positive expected
residual return, Alpha, and they manage their portfolio
Active Portfolio Management