基础班讲义49页 example 2 题干中提到" Berke has developed a time series model of the business cycle that uses a published LEI series as a key input", 原版书Reading3 课后题第13题题干也有类似的描述:“Cambo bases her equity market forecast on a time-series model using a composite index of leading indicators as the key input”。但是前者被认为是"the econometric modeling approach in conjunction with the LEI approach", 后者被认为是“The leading indicator–based approach”,这是为什么?