What is the purpose of a performance attribution model? In terms of the price-to-book (P/B) ratio, why are value stocks generally considered those with low P/B ratios? Comment on the following statements:

a. "All one needs to know about a portfolio manager's ability is to compare the return on the portfolio to the return on the benchmark."

b. "By looking at the difference between the portfolio return and the return on a benchmark, one can determine how a portfolio manager was able to outperform or underperform a benchmark.

c. "In establishing an investment policy, investors should ignore any liabilities and just select a market index that they want to outperform."