Question

How do you figure out assumptions for a two-tailed z test?

Answer 1

Assumptions for the z-test:
• The samples from each population must be independent of
one another.
• The populations from which the samples are taken must be
normally distributed and the population standard
deviations must be know, or the sample sizes must be large
(i.e. n1≥30 and n2≥30.

We can check the Normality assumptions by Drawing Histogram Or Normal Quantile plot.

If histogram shiws symmetrical shape then data is Normal.

Also if the quantile plot shows the linear line then the normality assumption is satisfied.