Whats the Average of “Not satisfactory” and “Outstanding”?

monkey_math.gif…or better yet what is the standard deviation? One of the issue i have come across well working on the stats plug-in for Moodle are grades that are not necessarily numerical values. Moodle allows for both text based grades and scales (witch are strings based on ones performance in a garble item) and it brings up the problem of how to work these grades in to common statics like mean, standard deviation, etc. For some like the mode this is simple enough to deal with and when a scale is used things like max and min grades are possible (by assigning a numerical value to each string in the scale) however something like standard deviation becomes meaningless at best (especially when expressed back in the same scale, the deviation between “Not satisfactory” and “Outstanding” is “Not satisfactory” and the average is “Satisfactory”??). What it might come down to is simply not having statistics for none number based grades or trying to find a method to express them threw a more sensible means.

Also i have made some progress on /grade/report/stats plug-in and have a demo on my test server that has the statistics per item per group as well as overall in a table. Still to do is to add options for dealing with things like hidden grades, selecting what grades users can see and cleaning up the look of the table. After that i can move on to working on the visual plug-in and the real fun can start. (I had ornignaly planed to talk about the desing of report/stats plug-in in this post but i am busy working on getting a more advanced demo up so it will have to wait and i shall have to get back to coding!)

2 Responses to “Whats the Average of “Not satisfactory” and “Outstanding”?”

  1. Tony Says:

    The problem applies not just to “non-number” data, but a lot of ordinal data as well. It’s not just that the mapping of words to numbers produces nonsensial measures (”Not satisfactory” deviation?), but that the ordinal relationship itself is likely wrong.

    Is the difference between not-satisfactory and satisfactory the same as another two adjacent adjectives? Not always.

    It might make more sense if more data came into play.

  2. HackerDan.com » grade/report/stats Says:

    […] can be displayed. You can also see in the last screen shot the issue mentioned in my last blog post here, about scales returning some interesting results for some statistics, tho if desired all scale […]

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