| The test for comparing proportions
is used to test whether differences in the
proportions of a characteristic that occur
in two samples are sufficient to prove that
the populations from which the samples were
taken are different. It is used when the
samples are large.
The hypothesis
is:
H0: the proportion is the
same in both populations
H1: the proportions are different/the
proportion is greater for process 1 than
process 2
The value of the Z statistic
is calculated from:
where:
p1 and p2: the
proportions in each sample
X1 and X2: the number
possessing the characteristic in each
sample
n1 and n2: the sample
size
The p-value
can be obtained from Excel using the function:
two-tail test: = (1 -
NORMSDIST(Z0))/2
Alternatively the critical
values can be found in the t-tables.
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