Scatter plot colored categories

[Michael Beddo]

I teach a statistics class and have recently acquired a TI nspire CX CAS calculator. Several of my students have one as well, though they don't know how to use it very much. I am learning so I can teach them.

We are discussing lurking variables in class. I have a data set in a spreadsheet in three columns: x, y, and z. The z value is a category with two values. I plot y vs x in a scatter plot where there appears to be a correlation, but what I want to do is change the color of points so that z=1 points are a different color than z=2 points, illustrating that the correlation is destroyed when the lurking variable z is controlled for.

I can't figure out how to do this. I tried splitting up into two lists but it seems I can't combine two scatter plots into one.

Any ideas?

Thanks

Mike

[alcoonslists]

Mike,

Divide your points this way:

Variable X - List all x values once
Variable Y1 - List those values for the given x for z=1
Variable Y2 - List those values for the given x for z=2
[Note: You can have both a Y1 and Y2 for a given x or just one of them]

Plot Y1 versus X

MENU/Plot Properties/Add Y Variable/Y2
Plot will have different colors for Y1 and Y2

This will at least get you the plot you want, but may not leave the data in the form you want for other things.

Hope this helps,

Al
-------------------------
Albert Coons
aco...@bbns.org
Buckingham Browne & Nichols School
Gerry's Landing Road
Cambridge, MA 02138
(617) 800-2264

AP Statistics Web Site: www.bbn-school.org/us/math/ap_stats

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[Michael Beddo]

Worked great! Thanks.