[gradebook2-dev] Questions about extra credit

[Jim Mezzanotte]

Hi all,

I've been exploring how the gradebook calculates extra credit points
when set up for weighted categories, and I wanted to share my
findings. Here's what I've determined about an extra credit item in a
weighted category (assuming the category is not itself set up to be
extra credit):

1. The points contributed by the EC item is determined by its weight
in the gradebook (i.e., relative weight x category weight). So if the
extra credit item's relative weight is 10% and the category weight is
30% (and assuming you score the EC item 100 out of 100), it will add 3
points to the calculated grade.

2. If one or more categories do not have any scored items, the EC
contribution to the calculated grade will be affected, since the tool
will ignore those categories and adjust the weights of categories with
scored items accordingly (to equal 100% weight). So when a category's
weight gets increased, so does the points contribution of an EC item
in the category.

3. The contribution of an EC item to the calculated grade is
constrained by the grade scale, even on the category level. In other
words, the points contributed by an EC item will never exceed the
total possible points the category contributes. So for example, if the
possible total of weighted scores for a category equals 30 points, and
the actual contribution is 28 points, the EC item will only contribute
2 points to the overall grade--even if it has been set to contribute
more.

The one thing I can't quite figure out is how scores are calculated
when you select "scale extra credit"--because when I selected this
setting, I saw no change in the behavior described above. I
anticipated that, with this setting selected, the EC contribution
would be unaffected by one or more categories not having any scored
items (since I assume the EC contribution would be scaled against
total possible, not scored items). But apparently not.

I also determined the following behavior when you add an extra-credit
weighted category (and do not select "scale extra credit")

1. The contribution of the category (and its items) to the calculated
grade remains constant--i.e., is unaffected by unscored items and
resulting adjustments to category weights.

2. EC contributions are not constrained by grade scale--and therefore
can result in a calculated grade that is higher than 100.

So for example, let's say you add an EC category, give it a 20% weight
in the gradebook, and then add two items, both with a relative weight
of 50%. You score each item 100 out of 100. Entering the score for one
item adds 10 points to the calculated grade; entering the score for
the second item adds another 10 points.

Here, I did in fact notice different behavior with "scale extra
credit" selected. If you select this setting and only enter a score
for one item, the contribution will actually be 20 points--the full
category amount. In other words, the behavior is identical to a non-EC
weighted category, when only one item is scored--the non-scored items
get ignored, the scored item gets a 100% relative weight.

So my unanswered EC questions are, how exactly does Gradebook2
calculate grades differently when "scale extra credit" is selected?
And, is this behavior with an extra credit category the only thing
that changes when you select the "scale extra credit" setting?

Apologies in advance for the long message, thanks in advance for any input--

Best,
Jim Mezzanotte
rSmart