Theoretical Question Operational Data What is Sample and what is population.

#1
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 as being the population's or if I should consider it to be just a sample.

Some analyses require me to use the population's variance and mean and I don't know if I should use the ones calculated from the data I have or if I should infer it from them.

I have 2 years data on clinic attendance and performance for several clinics and staff members.

Thanks for your help.