# What are these formulas and what is their purpose? n=(sigma^2)(Z_alpha/h^2); two more

##### New Member
I can't find reference to these formulas in the slides posted by my professor. I also can't find any versions of these formulas anywhere else online - guess my google-fu sucks.

I get what Z_alpha is (critical value), I know what sigma is (population standard deviation), and n I guess is the sample size. The hell is h? and w? and the delta?

http://i.imgur.com/9RgKmZ6.png?1

And what do these formulas achieve? Thank you for reading.

#### Dason

Re: What are these formulas and what is their purpose? n=(sigma^2)(Z_alpha/h^2); two

They're both sample size calculations. The first is when you know the population standard deviation (or are willing to assume a value for it), know what confidence level you want, and know how wide you want the interval to be. They call the width of the interval w. Sometimes people instead characterize this using the half-width (half the width of the interval) and they call that h.

The second does look to be a sample size calculation for a two sample z-test.