Contours/CIs

[jake_bParticipant]

Is it possible to plot either ellipses representing a particular confidence interval (esp useful with scatterplot matrices), and also contours representing local density?

 

thank you!

[dgteamModerator]

You can add error bars in various forms and those include ellipses.  This is based on values in the data table.  This article will explain more:

How to add error bars

We don’t have confidence intervals calculated but you can use the standard deviation and mean to calculate using a function.  I believe it is the tcdf.  If you need a specific example let us know. See Statistical Functions for more on these functions..

I’ll follow up in another response on the contours.

[dgteamModerator]

For the contours we have a new  Scalar field command that is in our pre-release Beta version. This can represent Scalar fields and also draws contours.  Any registered user can download and use the beta version.

Here is some manufactured data with x-y points that are binned using the Pivot command in both x and y to get the 2D density data in a regular grid.  The output from the Pivot is used as input to the Scalar command.

In the image shown, the contours from the scalar field are drawn to above the points.  Making the points transparent also really helps to convey the density visually.

Here is a video short that demonstrates this combination of commands:

DataGraph Beta Short: How to make a 2D Histogram and Scalar Field of Point Density

Throwing a lot at you in one response!  If these examples are not quite what you meant let us know.  You can also post an image if that might help.

[jake_bParticipant]

hi, many thanks for both responses. The contour-type plotting looks exactly what I had in mind (it might be nicer with more rounded lines, but that’s a quibble) – but I think for the moment I will not start playing with the beta version, until I gain at least minor competence with the existing version!

With respect to the CI ellipses, I had meant for groups of points, rather than error bars. I will try to add a picture to see if that makes it clearer, thanks.

[dgteamModerator]

These ellipses with varying orientation is not something DataGraph can do currently.  The closest thing would be when you show the error bars using the x and y direction and chose the “Single Line” option.  That can convey similar information but in line form, not as an ellipse.

We are interested in adding this functionality. Do you know what method was used to produce these particular shapes?

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