The criteria for credibility assessment
| Item | Assessment aspects | Results |
| 1 | Whether the anchor instrument directly addressed the patient’s perspective. | 0=No 1=Yes 2=Impossible to tell |
| 2 | Whether patients could easily understand the anchor instrument. | 0=Definitely no 1=Not so much 2=To a great extent 3=Definitely yes 4=Impossible to tell |
| 3 | The correlation between the anchor and the PROM.* | 0=Definitely no 1=Not so much 2=To a great extent 3=Definitely yes NR=Not reported |
| 4 | The precision of the MID estimation. | 0=Definitely no 1=Not so much 2=To a great extent 3=Definitely yes NR=Not reported |
| 5 | Whether the threshold or difference between groups on the anchor used to estimate the MID represented a small but important change. | 0=Definitely no 1=Not so much 2=To a great extent 3=Definitely yes NR=Not reported |
*For anchors with categorical scales the Spearman rather the Pearson’s correlation, is appropriate.
MID, minimal important difference; PROM, patient-reported outcome measure.