What does standard deviation actually tell you about a stock? Barchart’s John Rowland explains how Bollinger Bands use standard deviation around a 20-day moving average — and why expanding from two to ...

The S&P 500 Index (SPX) just closed outside of its Bollinger Bands, prompting Senior Quantitative Analyst Rocky White to dig into what this could mean for the stock market. Below, let's dive deeper ...