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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: Graphing Quadratic Interactions |

Date |
Tue, 16 Dec 2008 15:17:06 -0000 |

No, we can't erase that. Ronan has a good point, which I doubt is controversial anywhere, that just because you have 3 variables doesn't meet that you are best off with 3-D graphics. In particular if you have 3-D scatter, meaning a point cloud or swarm, 3-D graphics are not necessarily going to help you much. If you have 3 categorical variables, the same is likely to apply. But plenty of us have data that define surfaces, often quite smooth ones, and for that use any 2-D projections or summaries don't capture the whole thing well. And if your data don't define a surface, your model predictions often will. Nick n.j.cox@durham.ac.uk Martin Weiss " This is not true, and all of the good high-dimensional charts I can think of use only two dimensions to display the data." So we can erase this perennial grievance ("When will Stata be able to draw 3-D graphs"?) from future "wishes & grumbles"... Ronan Conroy On 16 Noll 2008, at 12:42, Nick Cox wrote: > It wasn't very clear what she wants. My guess was that she wants a > plot > of predicted response in terms of X4 and X5, adjusting for X1 ... > X3. As > mentioned on this list very frequently, Stata isn't serious at 3-D > graphics that might meet this need, whether contour plots or > perspective > views. What are often called 3D graphics are a small, and very poor, subset of the ways in which higher dimensional data can be displayed on a flat surface. Their immediate drawback is that of point of view. They represent a two-dimensional view of a three-dimensional object. Thus, the point of view must be carefully chosen if it is not to result in some interesting features being obscured, and there is no guarantee that any single view will show you all the features of your data. However, it is possible to display data in many dimensions on a flat surface, and we do this all the time. Use of -by- and -over- to display different groups in the same chart increases the number of dimensions while keeping all the data visible at once. . sysuse auto . stripplot mpg, by(foreign) over(rep78) bar This shows domestic and foreign cars as two graphs within the chart, allowing us to see a third dimension easily. You can, with a little ingenuity, increase the number of dimensions by using what Tufte calls 'small multiples' - a tiled arrangement of smaller graphs which follows a logical order. My own contribution to the field was making a chart that displayed age, sex, smoking, cholesterol, blood pressure and cardiovascular risk on a flat surface. The resulting chart is also technically a table, since it displays risk numerically as well as using a traffic-light colour system. You can see the thing in various places on the net, including Chance News http://www.dartmouth.edu/~chance/chance_news/recent_news/chance_news_13. 03.h tml#item10 I mention this because people assume that you need "3D" to show more than two dimensions. This is not true, and all of the good high- dimensional charts I can think of use only two dimensions to display the data. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Graphing Quadratic Interactions***From:*"Susanna Khavul" <skhavul@gmail.com>

**References**:**st: Graphing Quadratic Interactions***From:*"Susanna Khavul" <skhavul@gmail.com>

**Re: st: Graphing Quadratic Interactions***From:*Ronan Conroy <rconroy@rcsi.ie>

**RE: st: Graphing Quadratic Interactions***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**Re: st: Graphing Quadratic Interactions***From:*Ronan Conroy <rconroy@rcsi.ie>

**RE: st: Graphing Quadratic Interactions***From:*"Martin Weiss" <martin.weiss1@gmx.de>

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