Since peaking on July 20, the iShares Nasdaq Biotechnology ETF, the largest biotech exchange traded fund, is off 15.2 percent. That is a correction and a half. Biotech sneezing has helped the broader healthcare sector catch a hold. IBB is a cap-weighted ETF, resulting in its top four holdings, including the three aforementioned stocks, combining for over a third of the fund's weight. Overall, IBB's top 10 holdings combine for over 60 percent of the ETF's weight, according to issuer data. Some analysts believe the recent retrenchment experienced by the biotech sector is giving way to a buying opportunity.