As a stock market analyst, Janet Yellen makes a pretty good Federal Reserve chair.
Nearly a year ago, on July 16, 2014, Yellen famously warned of "substantially stretched" valuations in some biotech and social media stocks. However, her admonition carried little weight particularly in biotech, where a year of big deals and strong growth has pushed shares in the sector higher and higher.
In the past 12 months, the iShares Nasdaq Biotechnology exchange-traded fund has rallied 52 percent. Over the same period, the S&P 500 has gained just 9.7 percent and the Nasdaq as a whole is up about 20 percent.
While that doesn't necessarily mean biotech isn't overvalued, it does mean that investors who took Yellen's warnings as advice and bailed on the sector missed out in a big way. (Tweet this)