In: Statistics and Probability
Following is an example of a right tailed, one sample
t-test.
An engineer measured the Brinell hardness of 25 pieces of ductile
iron that were subcritically annealed. The resulting data set was
as given below:
170 | 167 | 174 | 179 | 179 |
156 | 163 | 156 | 187 | 156 |
183 | 179 | 174 | 179 | 170 |
156 | 187 | 179 | 183 | 174 |
187 | 167 | 159 | 170 | 179 |
The engineer hypothesized that the mean Brinell hardness of all such ductile iron pieces is greater than 170. Therefore, he was interested in testing the hypotheses:
H0 : μ = 170
HA : μ > 170
The level of significance is alpha = 0.05. Since the population
standard deviation is not known to us, we are to use the sample
standard deviation in its place.
The test statistic for our test will be of the form,
Here,
Therefore, T = 1.22
p-value =
Since p-value is greater than alpha = 0.05, we fail to reject the
null hypothesis and conclude that there is insufficient evidence,
at the alpha = 0.05 level, to suggest that the mean Brinell
hardness of all such ductile iron pieces is greater than 170.