The Two Sample
z Test is a hypothesis
test used to to compare the
means of two samples to see if it is feasible
that they come from the same population.
The test is used where the standard
deviation is known or where
the sample size is large (greater than 30).
The test requires that the population conforms
to a normal
distribution. The hypothesis
is:
H_{0} the population means are
equal
H_{1} the popular means are different
The test is:

sample means 
n_{1}, n_{2} 
sample sizes 
s_{1}, s_{2} 
sample standard deviations 
The pvalue
can be obtained from Excel using the function:
onetail test: = 1  NORMSDIST(Z_{0})
twotail test: = (1  NORMSDIST(Z_{0}))/2
Alternatively the critical values of the
z statistic can be found from tables. For
a one sided test:
α

0.10 
0.05 
0.025 
0.01 
Z_{α
}  1.28 
1.64 
1.96 
2.33 
For samples with less than 30 items see
the Two
Sample ttest
