1. **Problem Statement:**
Test if there has been an increase in the proportion of drivers who text while driving from last year (17%) to this year (29%) using a 99% confidence interval.
2. **Formula and Explanation:**
We use a two-proportion z-test to compare two population proportions.
The test statistic is:
$$z = \frac{\hat{p}_1 - \hat{p}_2}{\sqrt{p(1-p)\left(\frac{1}{n_1} + \frac{1}{n_2}\right)}}$$
where:
- $\hat{p}_1 = 0.29$ (this year), $\hat{p}_2 = 0.17$ (last year)
- $n_1 = n_2 = 1000$
- $p = \frac{x_1 + x_2}{n_1 + n_2}$ is the pooled proportion
3. **Calculate pooled proportion:**
$$x_1 = 0.29 \times 1000 = 290$$
$$x_2 = 0.17 \times 1000 = 170$$
$$p = \frac{290 + 170}{1000 + 1000} = \frac{460}{2000} = 0.23$$
4. **Calculate standard error:**
$$SE = \sqrt{0.23 \times (1 - 0.23) \times \left(\frac{1}{1000} + \frac{1}{1000}\right)} = \sqrt{0.23 \times 0.77 \times 0.002} = \sqrt{0.0003542} \approx 0.0188$$
5. **Calculate z-statistic:**
$$z = \frac{0.29 - 0.17}{0.0188} = \frac{0.12}{0.0188} \approx 6.38$$
6. **Determine critical z-value for 99% CI:**
For a one-tailed test at 99% confidence, critical value $z_{0.01} = 2.33$
7. **Decision:**
Since $6.38 > 2.33$, we reject the null hypothesis.
8. **Conclusion:**
There is sufficient evidence at the 99% confidence level to conclude that the proportion of drivers who text while driving has increased this year compared to last year.
Proportion Increase 58953B
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