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

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

Subject |
RE: st: overlaying two histograms (or distribution curves) |

Date |
Sun, 22 Nov 2009 15:28:30 -0000 |

For comparison of precisely two distributions -- especially when there is not a prior prejudice or hypothesis that we are expecting approximations to some named, equation-specified distribution -- I regard quantile-quantile plots as near optimal. They allow you to focus on both similarity and differences and to think directly in terms of what is being measured. Why is this graph form which is (a) information-rich (b) free of arbitrary assumptions (bin or kernel width, etc.) (c) easy to explain (d) easy to compute (e) well documented not enormously better known? See -qqplot-. Nick n.j.cox@durham.ac.uk Ariel Linden, DrPH Thank you both (Maarten and Austin) for all these choices I had not known about (violin, byhist, kdens). Austin, I don't have a known distribution per-se. I have two groups (treated and controls), and the outcome variables could follow any distribution. The motivation for this is to visually describe how the distribution of an outcome variable overlaps (or doesn't) between two groups. Date: Fri, 20 Nov 2009 10:47:06 -0500 From: Austin Nichols <austinnichols@gmail.com> Maarten-- I think that is the same graph I gave for comparison purposes, but I don't think it compares well with -byhist- unless one takes a bit more care on the -kdensity- side--the kernel density estimates should at least use the same bandwidths, and perhaps the same estimation points if we really wish to compare them. Other considerations might apply if Ariel told us something about the theoretical distribution of the variable filling the role of "price" (is it discrete? does it have a finite range?). * * 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**:**AW: st: overlaying two histograms (or distribution curves)***From:*"Martin Weiss" <martin.weiss1@gmx.de>

**References**:**Re: st: overlaying two histograms (or distribution curves)***From:*"Ariel Linden, DrPH" <ariel.linden@gmail.com>

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