Sector Index Funds refers to an index in which all constituent stocks belong to the same industry. For example, JETS is a sector index in which all industries in the index are airline stocks. The calculation method of this type of index can be price weighted or market value weighted. Most sector index funds are composed of 20 to 30 stocks.
部门指数指所有成份股都属于同一行业的指数，比如JETS就是一个部门指数该指数的行业全部都是航空相关成分股。这类指数的计算方法可以为价格加权或是市值加权，大部分部门指数由20到30只股票组成。