Difficulty level by content element.
| Content element | Sum of wrong answer selection rate ( |
Number of options (k) | Difficulty level |
| relative velocity and the principle of relativity | 398.3 | 17 | 23.4 |
| the principle of constancy of the speed of light | 114.8 | 8 | 14.4 |
| the relativity of simultaneity | 683.4 | 25 | 27.3 |
| time dilation | 461.3 | 21 | 22.0 |
| length contraction | 482.4 | 20 | 24.1 |