Chi Square Goodness
1. **State the problem:**
A sociologist wants to test if the distribution of preferred study methods among college students is equally likely using a Chi-square Goodness of Fit test with significance level $\alpha = 0.05$.
2. **Hypotheses:**
- Null hypothesis $H_0$: The distribution of preferred study methods is uniform (all methods equally likely).
- Alternative hypothesis $H_a$: The distribution of preferred study methods is not uniform.
3. **Expected probabilities:**
Since there are 6 study methods, each is expected to have probability $\frac{1}{6}$.
4. **Observed values:**
Roll a six-sided die 30 times to simulate observed counts for each method.
Assume the following observed counts (example):
- Group Study (1): $O_1 = 5$
- Solo Study (2): $O_2 = 4$
- Online Tutoring (3): $O_3 = 6$
- In-Person Tutoring (4): $O_4 = 7$
- Library Study (5): $O_5 = 3$
- Peer Teaching (6): $O_6 = 5$
5. **Expected counts:**
$$E_i = n \times p_i = 30 \times \frac{1}{6} = 5$$
for each category $i$.
6. **Create observed vs expected table:**
| Method | Observed ($O_i$) | Expected ($E_i$) |
|--------|------------------|------------------|
| 1 | 5 | 5 |
| 2 | 4 | 5 |
| 3 | 6 | 5 |
| 4 | 7 | 5 |
| 5 | 3 | 5 |
| 6 | 5 | 5 |
7. **Calculate Chi-square test statistic:**
$$\chi^2 = \sum_{i=1}^6 \frac{(O_i - E_i)^2}{E_i} = \frac{(5-5)^2}{5} + \frac{(4-5)^2}{5} + \frac{(6-5)^2}{5} + \frac{(7-5)^2}{5} + \frac{(3-5)^2}{5} + \frac{(5-5)^2}{5}$$
$$= 0 + \frac{1}{5} + \frac{1}{5} + \frac{4}{5} + \frac{4}{5} + 0 = \frac{10}{5} = 2$$
8. **Degrees of freedom:**
$$df = k - 1 = 6 - 1 = 5$$
9. **Find p-value:**
Using Chi-square distribution with $df=5$, $\chi^2=2$ gives a p-value approximately $0.85$ (high p-value).
10. **Conclusion:**
Since $p = 0.85 > \alpha = 0.05$, we fail to reject the null hypothesis.
**Interpretation:** There is not enough evidence to conclude that the preferred study methods are distributed unequally. The sociologist can say students use all study methods equally based on this test.