问题如下：
Compared with the
weighted average coupon rate of its underlying pool of mortgages, the pass-through rate on a mortgage
pass-through security is:
选项：
A.lower.
the same.
higher.
解释：
A is correct.
The coupon rate of a mortgage pass-through security is called the pass-through rate, whereas the mortgage rate
on the underlying pool of mortgages is calculated as a weighted average coupon
rate (WAC). The pass-through rate is lower than the WAC by an
amount equal to the servicing fee and other administrative fees.
mortgage组成的portfolio，每一笔mortgage都有一个贷款利率，WAC就是portfolio的加权平均贷款利率，MPS的coupon rate就是pass-through rate。请问MPS不也是一堆贷款分层，和加权平均不是一样的意思吗？还有服务费是哪里来的呢？为什么MPS没有服务费呢?请教一下，不太明白哈
您看看上述的公式哈，它们存在着上述的关系，