alignment of cases with categorical data

[traci_higgins@terc.edu]

For the categorical data if you plot let’s say, Sex and Body Part (any two categorical attributes, one with a few values one with a lot of values) the case dots line up weirdly depending on how you drop the attributes on to the graph. If you start by dragging Sex to the Y axis you are OK (see graph on the right). But if you start by dragging Sex to the X axis (see the graph on the left), the graph is hard to read because of how the case dots are aligned (shown here once I flipped attributes, but even before I flipped them, it was hard to read because it didn’t align against the axis). I’m wondering if this is a bug. …I pasted a picture from CODAP but when I submitted, it disappeared.

• This topic was modified 3 years, 8 months ago by . Reason: attach image as separate file

[Bill Finzer]

Hi Traci,

Thanks for this. I wonder if you could try again to upload the screen capture, or, if that doesn’t work, send it to me by email. There are a lot of alignment issues with dot charts and I want to be sure I understand what you’re referring to.

Alternatively, tell me how to reproduce the problem with a particular dataset.

Thanks,

Bill

[traci_higgins@terc.edu]

I sent an email with the screen shot. Basically I had a categorical attribute with two values (Sex) and a categorical attribute with many values (Part of the Body Injured) and when we create a graph it is much easier to read if we start by putting Sex on the Y axis. If you start by putting it on the Y axis the alignment of the dots showing the cases makes it hard to visually inspect. This is true even if you flip the attributes after the graph was created so that Sex is shown on the Y axis.

[Bill Finzer]

Thanks for this. The problem is to determine whether to stack the points in each cell vertically or horizontally. Perhaps we could make that decision heuristically based on cell dimensions. Or we could add (yet another) control in the ruler menu.

Stack Points

• Vertically
• Horizontally

Got a preference?

Thanks again,

Bill

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[traci_higgins@terc.edu]

I’m not sure–but here is my thinking–the question of aligning the dots vertically or horizontally would be confusing for kids with limited experience (it may be confusing to more experienced people as well–although they might be more apt to try both and figure out what works best). However, if a heuristically driven approach to aligning the dots was set as the default, but there was also a button that could be used to override it, that would probably be ideal.  Then again, I don’t know what work that would involve and it may be that for the vast majority of situations there is a heuristic that would work without needing a way to over-ride it. To be honest, I have never thought about this before!

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