1.能举例子讲一下one-stage cluster sampling和two-stage分别是怎么操作的吗？ 2.和stratified random sampling不一样具体在哪呢？

notes讲到T分布时候有一道练习题： which of the following is not a property of t-distribution? A.as the degree of freedom get larger, the variance approaches zero. B. it is defined by single parameter, the degree of freedom C. it has more probability in the tails and less at the peak than a standard distribution 为什么A不对，假设样本量增大到无限，到时候方差不就变成0了吗？

老师，请问这个题干中给出的CV左单尾、右单尾，和双尾的2.048为什么不是2倍的关系啊，因为阿法是固定的呀，df也是啊

题目重复

第十六题咋理解呀

解析看不懂“The investor is hedged against interest rate risk if the duration gap is zero; that is, the investor's investment horizon is equal to the bond's Macaulay duration. The investor is at risk of lower rates only if the duration gap is negative; that is, the investor's investment horizon is greater than the bond's Macaulay duration. In this case, coupon reinvestment risk dominates market price risk.”，

spread volatility什么意思？

那用什么来测试AB两项

面值就相当于未来的值，比发行价要更贴近当前价格吧？

这个题目跟第一个题目对比，为什么这个选择优先股的发行价而不是当前价格呢？