标题: Help: Calculating the Z-Score CFAI Material Reading 10 [打印本页] 作者: lxwarr30 时间: 2011-8-14 14:03 标题: Help: Calculating the Z-Score CFAI Material Reading 10
Good morning, everyone.
I'm having trouble understanding the Z-Score test statistic.
In the reading, a few examples, and the equation for calculating the Z-Score are shown as follows:
Z = (Sample Mean - Population Mean) / Standard Deviation
but there is another equation as follows:
Z = (Sample Mean - Population Mean) / Standard Error
What is the difference between the two equations? In what scenario is each used? If someone could help elabrote I would appreciate it.
Thanks so much,
Sean作者: Valores 时间: 2011-8-14 14:11
std error = std deviation / sqrt(n) <-- n is the size of the sample.
if u are using the population in its entirety - the std deviation can be used directly.
however if u are using a sample to estimate parameters about the population - since the size of the sample makes a difference - you need to use the std error.
in another part of the curriculum - you would come across another rule of thumb - that when n (size of the sample) > 30, you can use z-statistic. Otherwise u need to use the t-statistic.
