Question

Dear all, i'm a Brazilian student and i finishing my gruaduation. However, I need to finish my final project, which is about capital structure. I intend to define an optimization model of capital structure for Brazilian companies in each sector.
But a problem arose during the preparation of this work. When I researched historical series of the variables used in the CAPM and calculated its mean and standard deviation, i found a problem. I studied the brazilian market returns (Rm of the CAPM), and i got a standard deviation higher than the mean of this variable.