Proportion Z Test
1. **State the problem:** We want to test if the proportion of identity theft complaints in a state is higher than 23% based on a sample of 383 identity theft complaints out of 1450 total complaints, at a 9% significance level.
2. **Parameter:** The parameter $p$ represents the true proportion of all consumer complaints in the state that are for identity theft.
3. **Hypotheses:**
- Null hypothesis: $$H_0: p = 0.23$$
- Alternative hypothesis: $$H_A: p > 0.23$$
4. **Assumptions and conditions:**
- Sample size $n = 1450$
- Sample proportion $$\hat{p} = \frac{383}{1450}$$
- Check $np = 1450 \times 0.23 = 333.5 \geq 10$ (condition met)
- Check $n(1-p) = 1450 \times (1-0.23) = 1116.5 \geq 10$ (condition met)
- Population size $N = 1000000 \geq 20n$ (condition met)
5. **Test statistic formula:**
$$z = \frac{\hat{p} - p}{\sqrt{\frac{p(1-p)}{n}}}$$
6. **Calculate sample proportion:**
$$\hat{p} = \frac{383}{1450}$$
7. **Set up test statistic as a fraction:**
$$z = \frac{\frac{383}{1450} - \frac{23}{100}}{\sqrt{\frac{\frac{23}{100} \times \left(1 - \frac{23}{100}\right)}{1450}}}$$
8. **Calculate denominator:**
$$\sqrt{\frac{0.23 \times 0.77}{1450}} = \sqrt{\frac{0.1771}{1450}} = \sqrt{0.000122138} \approx 0.01105$$
9. **Calculate numerator:**
$$\frac{383}{1450} - 0.23 = 0.2641 - 0.23 = 0.0341$$
10. **Calculate z-value:**
$$z = \frac{0.0341}{0.01105} \approx 3.09$$
**Final answer:** The test statistic is approximately $$z = 3.09$$.
Since $z$ is positive and large, this suggests evidence that the proportion of identity theft complaints is greater than 23% at the 9% significance level.