A large mutual fund group such as Fidelity offers a variety of funds. They include sector funds that specialize in particular industries and index funds that simply invest in the market index.
Find first the standard deviation of returns on the Gidelity Spartan 500 index Fund, which replicates the S&P 500. Now find the standard deviations for different sector funds. Are they larger or smaller than the figure for the index fund? How do you interpret your findings?