推荐回答（1个）
通俗的讲，指数型基金就是它跟踪的指数中有哪些股票，它就主要买哪些股票。比如以上证180指数为跟踪目标的指数型基金，就主要买上证180指数的成分股;一个股票在上证180指数中的比例有多大，在跟踪上证180指数的指数型基金中比例也就大概有多大。
指数型基金可以分为两种，一种是纯粹的指数基金，它的资产几乎全部投入所跟踪的指数的成分股中，几乎永远是满仓，即使市场可以清晰看到在未来半年将持续下跌，它也保持满仓状态，不作积极型的行情判断。这种纯粹的指数型基金在我国还较难运作，因为首先，我国的有关法规规定，证券投资基金必须有20%的资产投资于国债，这样如果一只全部资产都投资于上证180指数成分股的指数型基金就是不可能的;同时，证券市场上不断有新股发行，多数新股在上市后能够给投资者带来一定的预期年化预期收益。如果是一只纯粹的上证180指数基金，那么它就只好放弃这一块的预期年化预期收益。
指数型基金的另外一种，就是指数增强型基金。这种基金是在纯粹的指数化投资的基础上，根据股票市场的具体情况，进行适当的调整。比如说，我国首只开放式指数型基金——华安上证180指数增强型基金，就表示会从三个方面进行适当的增强：一是调整权重。华安的基金经理在对行业、个股进行深入研究的基础上，可能对一些预计预期年化预期收益超过平均水平的行业或个股增加投资的比例，而对一些预计预期年化预期收益低于平均水平的行业或个股调低投资比例。二是股票替代。华安的基金经理会通过申购新股，适量投资于预期被纳入成分股的股票;用非成分股替代流动性很差的成分股等方法替代一些股票。三是仓位调节。在通常情况下，华安180将以75%作为自己的股票目标仓位;但在基金经理能够明确判断市场将经历一段长期下跌过程时，基金的股票投资仓位最低可调低至基金资产的50%。从这个意义上来看，指数增强型基金既能够发挥指数化投资的优点，又能够适当结合积极型投资理念的优点，取长补短，互相结合。在海外，指数增强型基金的发展也非常迅猛。
值得指出的是，对于指数增强型基金的增强部分也是有约束的。如华安上证180指数增强型基金，作为我国第一只开放式指数型基金，它首次设定了“跟踪偏离度指标”来控制增强性投资的偏离风险，对华安180的积极投资行为进行约束，其该指标的最大容忍值设定为0.5%。
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