Table 9 Spearman’s rank correlation results and comparison between used methods.
Pair of variables | Spearman’s rank correlation | Comparison with Pearson correlation | |||
|---|---|---|---|---|---|
Spearman’s R | t(N-2) | p-value | Differences between methods | Conclusions | |
Wear scar diameter WSD & Phosphorus | − 0.354 | − 1.36 | 0.20 | Large (∆R = 0.445) | Outliers inflate Pearson |
Wear scar diameter WSD & Zinc | − 0.264 | − 0.98 | 0.34 | Huge (∆R = 0.667) | Extreme distortion of Pearson |
Wear scar diameter WSD & Sulfur | − 0.810 | − 4.97 | < 0.05 | Small (∆R = 0.184) | Consistent confirmation of a strong association |
Wear scar diameter WSD & Calcium | − 0.304 | − 1.15 | 0.27 | Huge (∆R = 0.668) | Pearson completely distorted |
Wear scar diameter WSD & Soot | 0.304 | 1.15 | 0.27 | Moderate (∆R = 0.273) | Outliers affect Pearson |
Wear scar diameter WSD & Phos. antiwear | − 0.617 | − 2.82 | < 0.05 | Large (∆R = 0.370) | Only Spearman shows significance. Monotonic but nonlinear relationship |
