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From |
Maarten Buis <maartenlbuis@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: how to group variables into equal number groups |

Date |
Tue, 26 Mar 2013 16:07:57 +0100 |

On Tue, Mar 26, 2013 at 3:30 PM, Xixi Lin wrote: > I am trying to make independent variables into decile groups, and I > used xtile decile=x1 if Period==`z', nq(10); however, it turns out > that xtile does not make equal number of the 10 groups, is there any > way to force stata to divide them into equal number of obs or almost > equal number of obs? This is a problem of logic rather than programming: you can only split a set of observation in 10 groups of _exactly_ the same size if the number of observations is a multiple of 10. If you have 10 observations, you can split that up in 10 groups of 1 observation each, but what do you do if you have eleven observations? Another possible reason would be ties in the variable x1. Say your variable x1 has 4 observations with values 1, 1, 2, 3 and you want to split it up in exactly 4 groups. The number of observations is not a problem, as it is an exact multiple of 4, but how do you split up the first two observations in two groups? Since you report large deviations, that suggests to me that the last problem is the one that realy bites you. The sollution is to look at what the values are that are so heavily tied and see if they make sense. For example, in most western countries you would expect to see a huge spike at 40 in a question on the usual number of hours per week that a respondent works. Another example would be if you have a measure of occupational status, which people usually think of as continuous, you will still see large spikes at values that correspond to the status values assigned to very common occupations like nurses and teachers. It is this type of deeper understanding of your data that can guide you on what to do next, which will typically be not splitting up your variable in 10 equally sized groups. -- Maarten --------------------------------- Maarten L. Buis WZB Reichpietschufer 50 10785 Berlin Germany http://www.maartenbuis.nl --------------------------------- * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**References**:**st: how to group variables into equal number groups***From:*Xixi Lin <winnielxx@gmail.com>

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