The BA should consider the sample size for the validity of performance measures. The prepayment rates from the previous decade may not be representative of the current housing market conditions. A significant change in the market could render the old data irrelevant for predicting current prepayment behavior. Therefore, the BA should ensure that the sample size is large enough and relevant to the current market to provide a valid comparison.References: : BABOK Guide v3, Section 7.6 : Performance Measurement