Interaction Test
1. **Problem Statement:**
Test whether there is an interaction between vegetable varieties and fertilizers on the number of leaves per plant at a 95% confidence level using the given data.
2. **Data Setup:**
We have three vegetable varieties (V1, V2, V3), three fertilizers (F1, F2, F3), and three groups (Group I, II, III). The data is the number of leaves per plant.
3. **Statistical Method:**
We use a two-way ANOVA with interaction to test if the interaction effect between vegetable varieties and fertilizers is significant.
4. **ANOVA Model:**
$$Y_{ijk} = \mu + \alpha_i + \beta_j + (\alpha\beta)_{ij} + \gamma_k + \epsilon_{ijk}$$
where:
- $\mu$ is the overall mean,
- $\alpha_i$ is the effect of the $i^{th}$ vegetable variety,
- $\beta_j$ is the effect of the $j^{th}$ fertilizer,
- $(\alpha\beta)_{ij}$ is the interaction effect between variety $i$ and fertilizer $j$,
- $\gamma_k$ is the block (group) effect,
- $\epsilon_{ijk}$ is the random error.
5. **Calculate Means:**
Calculate the cell means, row means (varieties), column means (fertilizers), and overall mean.
6. **Sum of Squares:**
Calculate the following sums of squares:
- Total Sum of Squares (SST)
- Sum of Squares for Variety (SSV)
- Sum of Squares for Fertilizer (SSF)
- Sum of Squares for Interaction (SSI)
- Sum of Squares for Blocks (SSB)
- Sum of Squares for Error (SSE)
7. **Degrees of Freedom:**
- $df_{Variety} = 3 - 1 = 2$
- $df_{Fertilizer} = 3 - 1 = 2$
- $df_{Interaction} = (3-1)(3-1) = 4$
- $df_{Blocks} = 3 - 1 = 2$
- $df_{Error} = (3)(3)(3) - (2+2+4+2+1) = 27 - 11 = 16$
8. **Mean Squares:**
Calculate mean squares by dividing sums of squares by their respective degrees of freedom.
9. **F-Statistics:**
Calculate F-values for interaction:
$$F_{Interaction} = \frac{MSI}{MSE}$$
10. **Decision Rule:**
Compare $F_{Interaction}$ with critical value $F_{2,16,0.05}$. If $F_{Interaction} > F_{critical}$, reject null hypothesis of no interaction.
11. **Conclusion:**
Based on the calculated F-value and critical value, conclude whether there is a significant interaction between vegetable varieties and fertilizers at 95% confidence level.
**Note:** Detailed numerical calculations require summing and squaring the data values, which can be done using statistical software or by hand for exact values.