Stock screeners are automated tools used by investment companies to help clients select a portfolio of stocks to invest in. The table below lists the annualized percentage return on investment (as compared to the Standard & Poor's 500 Index) for 15 randomly selected stock screeners provided by the American Association of Individual Investors (AAII).

9.0.11.614.616.07.719.99.83.224.817.610.79.1

12.7-2.3

a.Find a 99% confidence interval for the average annualized percentage return on investment of all stock screeners provided by AAII. Interpret the result.

b.A negative annualized return reflects a stock portfolio that performed worse than the S&P 500. On average, do the AAII stock screeners perform worse or better than the S&P 500? Explain.