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Category weight when using drop the lowest x

Qi Dunsworth's picture
Thu, 2008-11-13 13:00 — Qi Dunsworth

I saw a gradebook built like the following:

  • Quizzes category intended to weigh 40%. It has 12 quizzes in it, 10 points each. The lowest 2 should be dropped.
  • Labs category intended to weigh 40%. It has 11 labs in it, 10 points each. The lowest 1 should be dropped.
  • One final exam in the Final category that should weigh 20%.

    My question is what number should be put in for the weight of category Quizzes and Labs? I would assume 100 points (after the 2 quizzes dropped) and 100 points (after the 1 lab dropped). But currently the prof. has 40 and 40 in - he must have treated these numbers as percentages, see attached. However, it seems to work. So should the weight be % or the sum of point values? Is there a rule to follow at all? Thanks!

    Qi

    AttachmentSize
    category weight.jpg17.25 KB

    • Comments

    Thu, 2008-11-13 14:10 — Jennifer Mullen
    Jennifer Mullen's picture

    Re: Category weight when using drop the lowest x

    Qi, you may find this KB article helpful.

    Short version: this instructor is doing the correct thing.

    The weights are, essentially, percentages of the overall grade and not points. When the gradebook is in percentage mode the final grade is calculated by adding the percentage of points earned in a category times its weight for all categories. Point values and drops are relevant only for calculating the overall average for a category.

    So, lets say a student in this course earns 100% on 6 quizzes, 80% on 4 quizzes, and 0% on 2 quizzes. The two zero scores are dropped. The average for the category is: ( (100*6) + (80*4) ) / 10 = 92%

    The lab and final categories are calculated the same way. Let's say the student earns 100% on labs and 80% on the final.

    Final grade is calculated, according to the screenshot, as:

    (.92 * .40) + (1.00 * .40) + (.80 * .20)
    = .368 + .400 + .16
    = .928
    = 92.8%

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