Severity grading and probability of a result being found within a normal healthy population for various z-score thresholds
| Threshold for z-score | Severity grading | Approximate chance of finding this result in a healthy population |
| <−1.645 | Mild | 1 in 20 |
| <−2 | Moderate | 1 in 40 |
| <−2.5 | Moderately severe | 1 in 150 |
| <−3 | Severe | 1 in 750 |
| <−4 | Very severe | 1 in 30 000 |
Adapted from Quanjer et al.51