Results of DIF analysis in pooled data (France, Italy, Poland, Spain, Sweden and UK)
| Testlet | Main effects: country (uniform DIF) | Interaction effects: class interval by country (non-uniform DIF) | ||||||
| Mean square | F-statistic | Degrees of freedom | P value* | Mean square | F-statistic | Degrees of freedom | P value* | |
| Function | 1.736 | 2.711 | 5 | 0.030 | 1.033 | 1.613 | 36 | 0.015 |
| Emotional | 1.777 | 3.297 | 5 | 0.011 | 0.574 | 1.065 | 36 | 0.371 |
| Sleep | 3.832 | 3.264 | 5 | 0.012 | 0.961 | 0.818 | 36 | 0.766 |
| Social | 9.603 | 15.839 | 5 | <0.001 | 0.706 | 1.165 | 36 | 0.240 |
| Pain | 1.627 | 1.680 | 5 | 0.153 | 0.978 | 1.010 | 36 | 0.455 |
*Significant Bonferroni adjusted P value ≤0.003 suggest presence of uniform DIF.
DIF, differential item functioning.