Turnitin rubrics: how the numbers work
Using a custom rubric in Grademark does throw up a few foibles to consider when moving from a grade descriptor or marking sheet. This post looks at the numbers that are used in order with consideration on how to adjust scale points to give a better alignment to midpoint of grade bands.
A rubric is basically a matrix where we can define the relative weights of criteria in relation to assignment total and use a scale to assign a value.
Here we have 4 weighted criteria and a 5pt scale (5=best, 1=worst) For any Criteria we first look at the weighting and scale values to determine the rubric score.
The rubric score is the criteria weighting x scale point value. Each scale point value is then converted to a percentage of the maximum scale value (5)
I find it useful to have a table that shows the rubric score and contribution of each ‘box’ as a guide before thinking about whether the point values need to be adjusted
We can see that if a students scored 4 on each criteria they would receive 80% (4/5) and so on
| 5 | 4 | 3 | 2 | 1 | |
|---|---|---|---|---|---|
| Criteria 1 : (50%) | 0.5*5=2.5
50% |
0.5*4=2
40% |
0.5*3=1.5
30% |
0.5*2=1
20% |
0.5*1=0.5
10% |
| Criteria 2 (30%) | 0.3*5=1.5
30% |
0.3*4=1.2
24% |
0.3*3=0.9
18% |
0.3*2=0.6
12% |
0.3*1=0.3
6% |
| Criteria 3 (15%) | 0.15*5=0.75
15% |
0.15*4=0.6
12% |
0.15*3=0.45
9% |
0.15*2=0.3
6% |
0.15*1=0.15
3% |
| Criteria 4 (5%) | 0.05*5=0.25
5% |
0.05*4=0.2
4% |
0.05*3=0.15
3% |
0.05*2=0.1
2% |
0.05*1=0.05
1% |
| Max Contribution to assignment | 100% | 80% | 60% | 40% | 20% |
If we wanted to adjust the rubric scores to more closely match a grade bands – rather than receiving 80% if scored second best on all criteria we want to award 70%, we would change the scale point from 4 to 3.5 (70% of 5), the weightings would remain the same and you would see a change in each point value and contribution.
However the biggest number is always going to result in the max grade for that criteria so it is likely you will need to adjust final grade in the top right box and remember to explain to students that rubric score/percentage is not the same as the final score/grade.
So 3.5 when substituted above would look like rubric scores (% contribution)
1.75/5=35%
1.05/5=21%
0.53/5=10.5%
0.18/5=3.5%
Note that whatever you do in Grademark you should consider how this is calculated in Moodle – a value is returned to Moodle on the Post Date of an assignment where the max value and weighting of the individual grade item needs to be set in order to calculate correctly.