# sample mean and variance

1. ### Confusion between z and t values

Hi, Alright so I have some confusion on when to use specific tests and the z vs t test. Given this example (not my homework) could someone please clarify. Alright say you have a random sample of size 200. You find the sample mean to be 10 and the sample standard deviation to be 5. What...
2. ### Theoretical Question Operational Data What is Sample and what is population.

Hi all. I'm working on operational data of clinical operations, attendance, performance and employee performance. I'm trying to use statistical methods to make regressions, correlations and predictions but I don't know if I should use the mean value and variance for the "sample" I have...
3. ### the third statistics independent with sample mean and variance

As we know, if X1, X2 ... XN are IID normal distribution, then the mean of the samples and the variance of the samples are independent. My question is, could we use X1, X2 ... XN to construct the third statistics, which independent with the sample mean and variance.