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Central composite design: terms and the corresponding coefficients
| Term | Coefficient | p-value |
|---|---|---|
| Constant | 195.0 | < 0.001 |
| Linear | < 0.001 | |
| X1 (N:C ratio) | − 61.9 | < 0.001 |
| X2 (FeCl3) | 12.7 | 0.251 |
| X3 (Olive oil) | 48.8 | < 0.001 |
| Interaction | < 0.001 | |
| X1X2 | 28.1 | 0.057 |
| X1X3 | − 10.9 | 0.450 |
| X2X3 | 39.8 | 0.009 |
| Quadratic | 0.015 | |
| X12 | − 64.3 | < 0.001 |
| X22 | 30.7 | 0.007 |
| X32 | − 9.7 | 0.368 |
| Lack-of-fit | 0.578 | |
| R2 (%) | 80.10 | |
| R2adj (%) | 73.24 | |
