There is always uncertainty about the future returns of an equity. This is the essence of market risk. Banks need to be able to estimate how returns in the future might look in order to estimate their market risk exposure. The shape of equity returns will be influenced by the standard deviation of returns. The bigger the standard deviation, the wider the possible distribution of future returns, and therefore, more market risk the bank is exposed to. Here, American Airlines has a wider distribution of returns than that of Kellogg's, whose values are more concentrated around the mean. So a position in American Airlines would be considered to have more market risk. Now that being said, American Airlines does have more upside as well as downside. Illustrating that risk can also have a positive element to it. Furthermore, if the future return distribution was modeled on some identifiable probability distribution, such as the normal distribution, then the bank can calculate probabilities. Future returns will be above or below certain levels.