参考答案：B

解析：

Hedge funds use a self-reporting mechanism that introduces a number of biases in data analysis. There is a self selection bias ( in which managers only report results if they are good) is one important example, but there are also historical biases (managers only report the funds once they are good and will not volunteer prior data that may have been poor) and a survivorship bias (bankrupt or defunct funds will not be reported so only strong funds are included in the hedge fund database). Consequently, investors need to be very careful about the amount of attention they lend to hedge fund data.