The near point of vision is the closest distance at which the eye can focus clearly on an object. A student measured the near point of vision for four different age groups.
Table 1 shows the results.
| Age of volunteers (years) | Near point distance (mm) | Mean near point distance (mm) | ||
|---|---|---|---|---|
| Volunteer 1 | Volunteer 2 | Volunteer 3 | ||
| 20 | 105 | 102 | 108 | 105 |
| 30 | 140 | 145 | 141 | 142 |
| 40 | 222 | 218 | 220 | 220 |
| 50 | 410 | 405 | 415 | 410 |
Give one conclusion that can be made from the data in Table 1.
