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In this course, author Barton Poulson takes a practical, visual, and non-mathematical approach to the basics of statistical concepts and data analysis in SPSS, the statistical package for business, government, research, and academic organization. From importing spreadsheets to creating regression models to exporting presentation graphics, this course covers all the basics, with an emphasis on clarity, interpretation, communicability, and application.
If you have three scale variables that you want to graph, then one interesting option in SPSS is a 3D scatterplot where you have variables on three different axes, the X and the Y and the Z axis. In theory it's a straightforward variation on the regular 2D scatterplot. In practice though, it can get a little confusing and this will become clear after we look at one. For this example I am going to stay with the Google Searches data and Searches.sav and I am going to chart the relationship between three particular search terms, between searches for SPSS, for business intelligence, and for the term "totally lost." To do this, I go up to Graphs in the menu bar and I click on Chart Builder.
I come down in the gallery to scatter, then I am going to choose the third one here which is a 3D scatterplot. Interestingly, there is an option here of adding a categorical variable on top of it all which actually makes it four variables depicted at once, but I am not going to work with that one right now. I am just going to show you what's called this the simple 3D scatter. I'll click on that, and drag it up to the canvas. Then I need to pick my three variables, the X and the Y and the Z, and what I am going to choose is SPSS as our Y axis, Business Intelligence as our X axis, and Totally Lost as the Z axis, and from there I can simply click OK.
When we first get the chart it's a rather chunky looking orthographic projection of a bunch of circles floating in what appears to be a 3D space. Unfortunately it's hard to read and there are two ways of getting some sense of depth in this. One doesn't work very well and the other one works slightly better. I will show you both. First, we're going to need to edit the chart by double-clicking on it and then I am going to clean things up a little bit by getting rid of the decimal places on the axes, click on those, then I come up to Number Format and I am just going to put 0 and press Apply.
I will do it for the other ones and then there is the last one. Okay, now to try to get a sense of depth here, one choice is to click on these then come over to Spikes and choose Floor and click Apply, and that I think you can tell is not helpful. We have a bunch of pinpoints here but it just seems to make things much more complicated. So I am going to click on those again, go back to Spikes, and deselect them.
On the other hand, we do have another option. Now, I am going to first take these markers. I am just going to make them solid so they are a little easier to see as we take care of things, and what I do to this is with a 3D chart you can actually add motion. You can make this dynamic chart. If I come over to the chart and I right -click on it, the second choice is this one, this says 3D Rotation. And what I can do now is see how the cursor is turned into a hand? I can click on that and I can start moving things around.
Now, it's kind of fun. I can see there is an outlier there of some kind, right over here, and I believe from past experience that is Washington, D.C. I can get state labels and confirm that. But right now what I am going to do is I am just moving this around and when it's moving you can get a sense of a three-dimensional cloud of data, and it's kind of a neat way to do it. The problem of course is it's really hard to read. I don't really know what's what except there seems to be an outlier there and there appears to be some kind of association between the variables.
I can see that there is an association in 3D, but it's hard to read. A rotating three-dimensional interactive scatterplot can be a lot of fun. You can even add a four-dimensional variable with colored markers and it helps you to identify cases that are multivariate outliers, and that is that have unusual combination of scores. On the other hand, the problem is once the 3D chart stops rotating, it becomes just another flat 2D chart that's very hard to read. And for this reason, a better option might be to employ what are called multiple static 2D charts in a scatterplot matrix which is what I will show you next.
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