NO.PZ202206070100000102
问题如下：
With respect to his answer to Brown’s question, O’Reilly is most likely:选项：
A.correct. B.incorrect with respect to asynchronism. C.incorrect with respect to variances and correlations.解释：
Solution
A is correct. O’Reilly’s answer is entirely correct as stated.
B is incorrect. O’Reilly’s answer is entirely correct as stated. High-frequency data are more sensitive to asynchronism.
C is incorrect. O’Reilly’s answer is entirely correct as stated. High-frequency data produce more precise variances and co-variances (and less precise means).
A是正确的。O’Reilly的回答完全正确。
B是错误的。高频数据对异步更加敏感，即高频数据更容易产生异步性的问题。比如用每天的数据观测美国和欧洲股票市场，因为两地存有时差，所以就会出现异步性。但如果是用月度数据观测，这种时差就可以忽略不计。
C是错误的。高频数据产生了更大容量的样本数据，所以能估计出更精确的方差和协方差。但是对于均值而言，只要用的历史数据，估计的数值就不太精确。这也是根据实务观测到的结果。
另一道题目链接：https://class.pzacademy.com/qa/150728
这类似题目中，答案指向是high-frequency data tend to produce lower correlation estimates
但是这道题中，题目指向是high-frequency data improves the precision of sample variances, covariances, and correlations but not the precision of the sample mean.
所以我想请教的是，是我的理解有问题，还是这两个结论是矛盾的？
