Tests of Proportions (2 of 4)
- The fourth step is to compute p, the probability
(or probability value). It is the probability of
obtaining a difference between the proportion and the value specified
by the null hypothesis as large or larger than the difference observed
in the experiment. The general formula for significance
testing
as applied to this problem If p is greater than π then the formula is:
.
If p is less than π then the formula is:
Note that the correction always makes z smaller.
N is the sample size and σpis the standard error of a proportion. The formula for a standard error of a proportion is:
.
The term
is the correction
for continuity. For the present problem,
Therefore,
A z table can be used to determine that the two-tailed probability value for a z of 2.3 is 0.0214.