# Population Variance - do we ever know this in real life?

I know what we have different situations when population variance is known or unknown. But I find it confusing that when we will ever know the population variance in our real life? You would need to ask the entire population to know that right? Then the example in this course - you have a sample data set with population std known - is this realistic in real life with "population std known"? Thank you in advance!

Hey Xiaoshi

As far as I know, the known population variance is merely for educational purposes like this exercise.

it's normal for a university to have the data of all the students every year, so yes in rare situations you can have the population variance

if we have the population variance shouldn't we also have population mean ?

I think most of the time we will have to work on data without knowing its population parameters :)