Assume you have an unbiased mean estimate of the annual rate of return on S&P 500 (25 years of historical data). True value of mean is unknown. To find an unbiased estimate of the value of S&P 500 portfolio 10 years from now, you need to compound the mean return estimate (from 25 years of data) over 10 years.

Is this true of false? Can you please explain why.