3. Exercise 15.38. Cooking vegetables in different pots. Let's first concentrate on the 12 observations for the vegetable dish. Does the vegetable dish vary in iron content when cooked in aluminum, clay, and iron pots? Pot Rep Dish Aluminum 1 Aluminum 2 Aluminum 3 Aluminum 4 Clay Clay Clay Clay Iron Iron Iron Iron 123 4 1 2 3 4 Iron content vegetable 1.03 vegetable 1.53 vegetable 1.07 vegetable 1.30 vegetable 1.55 vegetable 0.79 vegetable 1.68 vegetable 3.52 vegetable 2.45 vegetable 2.99 vegetable 2.80 vegetable 2.92 (a) Check the conditions for one-way ANOVA. Which requirements are a bit dubious in this setting? (b) Instead of using ANOVA, using a nonparametric method. Summarize your conclusions about the effect of pot material on the iron content of the vegetable dish.

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### Exercise 15.38: Cooking Vegetables in Different Pots

Let's first examine the data for the 12 observations of the vegetable dish. We are interested in determining whether the iron content in the vegetable dish varies when cooked in aluminum, clay, and iron pots.

#### Observations Table

| Pot        | Rep | Dish       | Iron content |
|------------|-----|------------|--------------|
| Aluminum   | 1   | vegetable  | 1.03         |
| Aluminum   | 2   | vegetable  | 1.53         |
| Aluminum   | 3   | vegetable  | 1.07         |
| Aluminum   | 4   | vegetable  | 1.30         |
| Clay       | 1   | vegetable  | 1.55         |
| Clay       | 2   | vegetable  | 0.79         |
| Clay       | 3   | vegetable  | 1.68         |
| Clay       | 4   | vegetable  | 3.52         |
| Iron       | 1   | vegetable  | 2.45         |
| Iron       | 2   | vegetable  | 2.99         |
| Iron       | 3   | vegetable  | 2.80         |
| Iron       | 4   | vegetable  | 2.92         |

#### Analysis Questions

(a) **Check the conditions for one-way ANOVA. Which requirements are a bit dubious in this setting?**
- One-way ANOVA assumptions:
  1. **Independence:** The observations must be independent of each other.
  2. **Normality:** The distribution of the residuals should be approximately normal.
  3. **Homogeneity of variances:** The variances among the groups should be approximately equal.

   In this setting, we need to check these assumptions:
   - **Independence** might be assumed because the replications are likely done separately.
   - **Normality** might be questionable due to the small sample size (n=4 for each group). A normality test such as the Shapiro-Wilk test or examining a Q-Q plot may be needed.
   - **Homogeneity of variances** can be checked using Levene's test or examining the variance in each group to ensure they are roughly equal.

(b) **Instead of using ANOVA, consider using a nonparametric method
Transcribed Image Text:### Exercise 15.38: Cooking Vegetables in Different Pots Let's first examine the data for the 12 observations of the vegetable dish. We are interested in determining whether the iron content in the vegetable dish varies when cooked in aluminum, clay, and iron pots. #### Observations Table | Pot | Rep | Dish | Iron content | |------------|-----|------------|--------------| | Aluminum | 1 | vegetable | 1.03 | | Aluminum | 2 | vegetable | 1.53 | | Aluminum | 3 | vegetable | 1.07 | | Aluminum | 4 | vegetable | 1.30 | | Clay | 1 | vegetable | 1.55 | | Clay | 2 | vegetable | 0.79 | | Clay | 3 | vegetable | 1.68 | | Clay | 4 | vegetable | 3.52 | | Iron | 1 | vegetable | 2.45 | | Iron | 2 | vegetable | 2.99 | | Iron | 3 | vegetable | 2.80 | | Iron | 4 | vegetable | 2.92 | #### Analysis Questions (a) **Check the conditions for one-way ANOVA. Which requirements are a bit dubious in this setting?** - One-way ANOVA assumptions: 1. **Independence:** The observations must be independent of each other. 2. **Normality:** The distribution of the residuals should be approximately normal. 3. **Homogeneity of variances:** The variances among the groups should be approximately equal. In this setting, we need to check these assumptions: - **Independence** might be assumed because the replications are likely done separately. - **Normality** might be questionable due to the small sample size (n=4 for each group). A normality test such as the Shapiro-Wilk test or examining a Q-Q plot may be needed. - **Homogeneity of variances** can be checked using Levene's test or examining the variance in each group to ensure they are roughly equal. (b) **Instead of using ANOVA, consider using a nonparametric method
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