It has been said, and it is more often than not true, that flows data for exchange data is not a predictor of future performance, but rather a sign of investors chasing past performance.

When it comes to once beloved biotechnology ETFs, it is not debatable that the group’s recent plunge has prompted investors to depart for greener pastures. Since February 28, only one of the five biotech ETFs, the First Trust NYSE Arca Biotechnology Index Fund (NYSEArca: FBT), has seen flows. Over the same time, investors have pulled almost $324 million from the iShares Nasdaq Biotechnology ETF (NasdaqGM: IBB), the largest biotech ETF. [Biotech ETFs Fighting for Their Lives]

“Recently, investors have begun to question whether biotechnology stocks are in a bubble and whether the companies developing complex and often expensive medicines are worth their high valuations. After gaining 11 percent in January and February, the Standard & Poor’s 500 Biotechnology Index has fallen 11 percent since March 3,” reports Drew Armstrong for Bloomberg.

In a sign of how intense the sell-off in biotech stocks and ETFs has been over the past six weeks, FBT is the best performer among the five major biotech ETFs since Feb. 28 with a loss of 10.9%. IBB and the Market Vectors Biotech ETF (NYSEArca: BBH) are both down more than 14% over that time. Outflows from IBB, BBH, the PowerShares Dynamic Biotechnology & Genome Portfolio (NYSEArca: PBE) and the SPDR S&P Biotech ETF (NYSEArca: XBI) since the end of February total more than $550 million.

Conversely, the ProShares Ultrashort Nasdaq Biotechnology (NasdaqGM: BIS) has hauled in $21.4 million over that time. That does not sound like much, but consider this: BIS had just $7.76 million in assets at the end of last year.[Inverse Biotech ETF Gains Acclaim]