In: Statistics and Probability
In 2016, it was reported that 16% of 500 Utah families had incomes below the poverty level. At the same time, 11.3% of 450 Wyoming families had incomes below the poverty level. You need to find out if there was a significant difference in proportion of families with incomes below the poverty level in these two states. Determine the critical values (use 5% significance level).alculate the p-value for the test. (g) Assess the strength of your decision in part (d) using the p-value. (h) Calculate a 95% confidence interval for the difference between the two corresponding population proportions (see pages 280-281 in the Blue Book). (i) Which state has a higher proportion of families with incomes below the poverty level, and by how
For sample 1, N1=500, the sample proportion is
For sample 2, N2=450, the sample proportion is
The value of the pooled proportion is computed as
Also, the given significance level is α=0.05.
(1) Null and Alternative Hypotheses
The following null and alternative hypotheses need to be tested:
Ho:
Ha:
This corresponds to a two-tailed test, for which a z-test for two population proportions needs to be conducted.
(2) Rejection Region
Based on the information provided, the significance level is α=0.05, and the critical value for a two-tailed test is zc=1.96.
(3) Test Statistics
The z-statistic is computed as follows:
(4) Decision about the null hypothesis
Since it is observed that ∣z∣=2.083>zc=1.96, it is then concluded that the null hypothesis is rejected.
Using the P-value approach: The p-value is p=0.0373, and since p=0.0373<0.05, it is concluded that the null hypothesis is rejected.
(5) Conclusion
It is concluded that the null hypothesis Ho is rejected. Therefore, there is enough evidence to claim that population proportion p1 is different than p2, at the 0.05 significance level.
Confidence Interval
The 95% confidence interval for p1−p2 is: 0.003<p1−p2<0.09
Utah has a higher proportion of families with incomes below the
poverty level, between 0.003<p1−p2<0.09.
Graphically
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