StdDev displaying very wrong value on a graph

Tagged: graph ruler standard deviation

This topic has 1 reply, 1 voice, and was last updated 3 years, 4 months ago by Bill Finzer.

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August 2, 2021 at 7:07 pm #6608 Score: 0

Andrew Ross
Participant

Starting with this dataset, https://codap.concord.org/app/static/dg/en/cert/index.html#shared=159770

I added a graph, dragged GradRate_LI to the x-axis, and used the Ruler icon in the toolbar to show the mean and SD. The mean displays correctly as 74 initially, and shows more precision (73.97) if you make the graph wider, and that’s good. However, the SD shows “+/- SD, 67” when the true standard deviation is 6.97 (as calculated by stdDev(GradRate_LI) ). I’m pretty sure the SD isn’t much above 10 for this dataset, so 6.97 is believable; 67 is not.

Here is an attempt to show the result: https://codap.concord.org/app/static/dg/en/cert/index.html#shared=https%3A%2F%2Fcfm-shared.concord.org%2FkV84y7W77w9t3DKisyZ9%2Ffile.json

I tried it on both Firefox and Chrome and got the same thing. Making the graph wider did not change the value that the SD displays. I will try to paste a screenshot here:

August 4, 2021 at 10:20 pm #6615

Bill Finzer
Keymaster

Hello Andrew,

Thank you very much for this important bug report! We’ll have it fixed in the next build.

Bill
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