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

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

Subject |
RE: st: even categories |

Date |
Tue, 14 Oct 2008 15:57:16 +0100 |

I agree with Maarten. Unequal frequencies typically reflect the existence of ties. Here is a simple example: sysuse auto xtile cmpg = mpg, n(4) tab cmpg su mpg, detail dotplot mpg, yli(18 20 25) A larger question is why categorise at all? Usually this is just throwing away information. If the difficulty is felt to be working with a measured variable, statistics has plenty of solutions for that; in fact, it's a feature. Nick n.j.cox@durham.ac.uk Maarten buis If -xtile- does not give you categories with approximately the same number of observations then that would indicate that there are some extreme ties or spikes in your data. With such extreme ties almost any automated procedure will fail. In that case you should have a good look at your data and see if there is some substantive reason behind this clustering. You could use for instance -spikeplot var-, where var is the variable in question. For example, if you ask people how many hours a week they work the answer will typically be a multiple of 4 (i.e. half an 8-hour workday) and there will be a spike at 36 or 38 or 40 depending on what's considered full time, which differs between the countries. Once you have found such a substantive reason I would try to use that to classify people into different categories. Philip Sinclair > I would like to make a categorical variable with approximately even > order categories, but I have found > that xtile does not always quite do the trick. Please is there an > alternative? * * 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/

**References**:**st: even categories***From:*"Philip Sinclair" <sinclairp@Cardiff.ac.uk>

**Re: st: even categories***From:*Maarten buis <maartenbuis@yahoo.co.uk>

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