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Re: st: visualization?


From   Gabi Huiber <ghuiber@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: visualization?
Date   Wed, 5 Oct 2011 14:58:12 -0400

Nick, thank you for this list. It's a useful refresher.

Regarding 2 and 6: I didn't know that transparency was on a wish list,
but I'm glad to hear it is. I once saw a nice demonstration of ggplot2
on r-blogger.com: markers of slightly less than 100% transparency
acted like disks of glass. One of them looks barely visible; the more
of them you stack, the darker the pile. This gives a very nice
gradient over a scattershot. It's prettier than the current
recommended workaround that we use hollow circles.

Gabi

On Fri, Sep 30, 2011 at 10:23 AM, Nick Cox <njcoxstata@gmail.com> wrote:
> Do you mean Vince Viggins? Sounds like a Dickens character. We saw
> Vince Wiggins at the London meeting.
>
> We are starting with these suggestions. I'll add numbers for convenience.
>
> 1. If one of the variables is positively skewed, consider plotting
> that axis on a log scale.
>
> 2. If there are a lot of data points (e.g., n > 1000), adopt a
> different strategy such as using some form of partial transparency, or
> sampling the data;
>
> 3. If one of the variables takes on a limited number of discrete
> categories, consider using a jitter or a sunflower plot;
>
> 4. If there are three or more variables, consider using a scatterplot matrix;
>
> 5. Fitting some form of trend line is often useful;
>
> 6. Adjust the size of the plotting character to the sample size (for
> bigger n, use a smaller plotting character);
>
> Random comments
>
> 1. I take this as standard. I'll add a plea for consideration of any
> reasonable non-linear scale, labelled in the original units!
>
> 2 and 6. Transparency is on some wishlists for Stata. With lots of
> data, you go not only for smaller symbols but more open ones and use
> lighter colors.
>
> 3. I've played with sunflower plots and gone off them. But if you want
> to try them, note that they are undocumented [sic] at -help twoway
> sunflower-. For highly discrete or even categorical variables, I like
> my -tabplot- (SSC).
>
> 4. Agree, although that does not rule some projection from a
> multivariate analysis being helpful too.
>
> 5. Yes, if "trend" means "smooth". Some special smooths were published in
>
> SJ-10-1 gr0021_1  . . . . . . . . . .  Software update for doublesm and diagsm
>        (help doublesm, diagsm, polarsm if installed) . . . . . . .  N. J. Cox
>        Q1/10   SJ 10(1):164
>        option to carry out smoothing using restricted cubic splines
>        added to doublesm and diagsm
>
> SJ-5-4  gr0021  . . . . . . .  Speaking Stata: Smoothing in various directions
>        (help doublesm, diagsm, polarsm if installed) . . . . . . .  N. J. Cox
>        Q4/05   SJ 5(4):574--593
>        discusses exploratory tools for determining the structure
>        of bivariate data
>
> Some possible additions:
>
> 7. About 1980, there was a sudden fashion for adding convex hulls,
> which faded away quickly. I remember often doing it with a pencil on
> lineprinter output. But Allan Reese has a nice implementation on SSC
> as -cvxhull-. On occasion that helps a lot.
>
> 8. When you have a categorical subdivision, try out both several
> categories superimposed and a -by()- option to give separate plots. A
> third strategy is given in
>
> SJ-10-4 gr0046  . . . . . . . . . . . . . . . Speaking Stata: Graphing subsets
>        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
>        Q4/10   SJ 10(4):670--681                                (no commands)
>        explores graphical comparison of results for two or more
>        subsets where each subset is plotted in a separate panel,
>        with the rest of the data as a backdrop
>
> Nick
>
> On Fri, Sep 30, 2011 at 2:56 PM, Stas Kolenikov <skolenik@gmail.com> wrote:
>
>> There was an interesting question on data visualization on
>> Stats.StackExchange (http://stats.stackexchange.com/q/13148/5739):
>> what are the efficient strategies for tweaking scatterplots depending
>> on the data needs? Too much data make it clogged, too little data such
>> as ordinal make it too chunky, too skewed data makes it sit in one
>> corner, and there are a multitude of other things that needs to be
>> adjusted to make the display really informative.
>>
>> I would be especially curious to hear from Nick Cox and Michael
>> Mitchell, I guess, as the greatest contributors to Stata graphics (and
>> of course Vince V, but I don't think I've seen him on the list for a
>> while).
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