Standard deviation is a metric that shows the variability of a security’s returns over time. It can be used to gauge volatility based on past performance and compare a future return to past returns.

Standard deviation is a common statistical measurement and is defined by Oxford Dictionaries as: ‘A quantity expressing by how much the members of a group differ from the mean value for the group.’ In ...

In response to my article, Is the Stock Market Too Concentrated?, which relied upon standard-deviation calculations to assess investment risk, a reader wrote: “My problem [with your argument] is ...