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Re: st: RE: running -ktau- and storing its results for each observation


From   "Kelvin Foo" <kelvinski@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: running -ktau- and storing its results for each observation
Date   Fri, 17 Nov 2006 22:44:18 +0000

Thanks Nick, your code did the job.

Kelvin.


On 11/17/06, Nick Cox <n.j.cox@durham.ac.uk> wrote:
I agree that you would be better off with the data
-reshape-d to long.

After that one standard protocol is of this form

levelsof id, local(ids)

gen corr = .

qui foreach i of local ids {
       ktau rank90 rank05 if id == `i'
       replace corr = r(tau_a) if id == `i'
}

After that, each correlation for each individual is necessarily
repeated for each observation for that individual.
You can tag just one observation from each group
using -egen, tag()-.

For more on -foreach- see for example

[P]     foreach . . . . . . . . . . . . . . . . . . . . . . .  Loop over items
       (help foreach)

FAQ     . . . . . . . . . . Making foreach go through all values of a variable
       8/05    Is there a way to tell Stata to try all values of a
               particular variable in a foreach statement without
               specifying them?
               http://www.stata.com/support/faqs/data/foreach.html

FAQ     . . . . . . . . .  Counting distinct strings across a set of variables
       7/04    How do I count the number of distinct strings
               across a set of variables?
               http://www.stata.com/support/faqs/data/distinctstrings.html

FAQ     . . . . . . . . . . . . . . Getting nice time of day labels on a graph
       9/03    How can I get "nice" time of day labels on a graph?
               http://www.stata.com/support/faqs/graphics/nicetime.html

Example . . . . Stata learning module:  Working across variables using foreach
       . . . . . . . . . . . . . . . . . .  UCLA Academic Technology Services
       8/03    http://www.ats.ucla.edu/stat/stata/modules/acrossvars.htm

SJ-3-2  pr0009  . . . . . . . . . . . . . Speaking Stata:  Problems with lists
       Q2/03   SJ 3(2):185--202                                 (no commands)
       discusses ways of working through lists held in macros

SJ-2-2  pr0005  . . . . . .  Speaking Stata:  How to face lists with fortitude
       Q2/02   SJ 2(2):202--222                                 (no commands)
       demonstrates the usefulness of for, foreach, forvalues, and
       local macros for interactive (non programming) tasks

There are also other versions of the last on the internet, as a Google
will show.

Nick
n.j.cox@durham.ac.uk

Kelvin Foo

> I have a dataset where individuals rank items from 1 to 10 in the
> years 1990 and 2005. I would like to find the Kendall's tau statistic
> for each individual's rankings of items between these two years, and
> store the results in a new variable. In my dataset, the individuals
> are the observations and the rankings are stored in 20 variables,
> named A_90, B_90... J_90, A_05, B_05,.. J_05. A to J are the 10 items
> and '90', '05' are the years.
>
> How can I carry out this task?
>
> My guess is to first use -reshape- to have 1990's rankings stored in
> one variable (rank90), and 2005's rankings in another variable
> (rank05). Each individual would have an identifier number associated
> with him, and this will appear 10 times in the reshaped long format.
>
> Next, I was thinking of running
>
> generate correl=. // variable for storing Kendall tau results
> by identifier: ktau rank90 rank05
>
> But how do I get Stata to store the r(tau_a) result in correl for each
> individual before moving on to the next one?
>
> Or is there an alternative way in which I can find the Kendall tau for
> each observation, given that my rankings are stored across different
> variables?

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