IBB holds biotechnology and pharmaceutical companies listed in the US, weighted by market capitalization, so large profitable companies such as Amgen, Gilead and Vertex have the largest weights. This gives it more exposure to established companies than the equal-weighted XBI, and generally lower volatility. Results depend on drug development outcomes, pricing policy and regulation, and takeover activity. The fund holds a few hundred stocks, but the largest holdings have a significant effect on returns.
