Question #341737

In a study to estimate the proportion of smokers among the residents in a certain city and its suburbs, it is found that 24 of 104 urban residents are smokers, while 34 of 108 suburban residents are smokers.


1
Expert's answer
2022-05-17T11:11:23-0400

The value of the pooled proportion is computed as


pˉ=X1+X2n1+n2=24+34104+108=29106\bar{p}=\dfrac{X_1+X_2}{n_1+n_2}=\dfrac{24+34}{104+108}=\dfrac{29}{106}

The following null and alternative hypotheses for the population proportion needs to be tested:

H0:p1=p2H_0:p_1=p_2

Ha:p1p2H_a:p_1\not=p_2

This corresponds to a two-tailed test, and a z-test for two population proportions will be used.

Based on the information provided, the significance level is α=0.05,\alpha = 0.05, and the critical value for a two-tailed test iszc=1.96.z_c = 1.96.

The rejection region for this two-tailed test is R={z:z>1.96}.R = \{z: |z| > 1.96\}.

The z-statistic is computed as follows:


z=p^1p^2pˉ(1pˉ)(1/n1+1/n2)z=\dfrac{\hat{p}_1-\hat{p}_2}{\sqrt{\bar{p}(1-\bar{p})(1/n_1+1/n_2)}}

=241043410829106(129106)(1/104+1/108)=\dfrac{\dfrac{24}{104}-\dfrac{34}{108}}{\sqrt{\dfrac{29}{106}(1-\dfrac{29}{106})(1/104+1/108)}}

=1.380342=-1.380342

Since it is observed that z=1.3803421.96=zc,|z| = 1.380342 \le 1.96=z_c , it is then concluded that the null hypothesis is not rejected.

Using the P-value approach:

The p-value is p=2P(Z<1.380342)=0.167481,p=2P(Z<-1.380342)=0.167481, and since p=0.167481>0.05=α,p=0.167481>0.05=\alpha, it is concluded that the null hypothesis is not rejected.

Therefore, there is not enough evidence to claim that the population proportion p1p_1 is different than p2,p_2, at the α=0.05\alpha = 0.05 significance level.


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