Experience it yourself:
- Invite four teachers in a room to score 20 essays, math problems or lab reports using a 10 point scale.
- Look at the diversity of scores among the 20 essays, math problems or lab reports.
- Now, ask the same four teachers to score the same 20 student work samples using a *4-point scale.
- Once again, examine the diversity of scores among the 20 essays, math problems or lab reports.
*The same exercise could be done using a 3-point scale or a 5-point scale.
I (sort of) gave this exercise a try once and concluded "When using a smaller scale (4 scoring possibilities vs. 10 scoring possibilities), mathematical logic kicks in: humans are more consistent when given fewer scoring possibilities."