Error in the results of returns-based style analysis is often explained as "noise in the data."  In fact substantial error may be caused by changes in portfolio exposure even when no noise is present in the data.  This second form of error-dynamic noise-often occurs as the result of tactical or strategic asset reallocation, or from change in the investment style.  Two techniques that can be effective in dealing with dynamic noise and improve accuracy of estimate are the use of a centered regression window and the weighting of returns.