Z-score (when to use standard deviation and when to use standard error)

Hi Analystforum

Can you help me understand when to use standard deviation vs. standard error, when calculating a z-score?

I have seen both

(1) z = (x-mu) / sigma and (2) z = (x-mu) / (sigma/sqrt(n))


There’s a thread somewhere where Magician and yours truly had detailed the topic threadbare.

Dropping a hint : sample has sampling error that when standardised forms standard error. A population cannot have standard error. Practically it is impossible to work with population though qs. May come with either population or sample standard deviation given. Do refer to that thread. Your doubts will be ironed out.