español

In this post I leave you a simple Stata code that generates a table of means differences (between 2 groups) for a set of variables. It looks like this:

A table of this type will be useful, for example, when the aim is to compare a treatment group and a control group across a series of variables.

Stata has the ttest command to perform tests of this kind, but does not incorporate, as far as I know, a functionality for exporting a table of multiple tests.

This code tests a large number of variables, with the advantage that it  generates and exports a publication-style table. The table is saved in a text (.txt) file. Then, I usually import this table into Excel (insert> data> text) for final retouching before copying it to the final document. I leave you the Excel template as well. For simplicity, asterisks for significant statistics, parentheses and brackets are added – also automatically – by the Excel template.

From the statistical point of view, it might be worth mentioning the subject of false-discovery rates, which could be relevant in an application of this type. I will leave it for for a future post.

You can test the code with this database, which contains the results of a survey for two groups (one “treatment” and one “control”) of individuals on urban attributes’ quality .

If you find it useful, or for comments and suggestions please leave me a comment!

[sourcecode language=”text” firstline=”1″ highlight=”1,3,5,7″ padlinenumbers=”false”] *Define folder for text file output
cd "C:\Users\Ricardo Pasquini\Documents\otros"
* A global macro handles the names of the multiple variables
global TTESTVARS "veredalimpia_nota verdes_nota ilum_nota nocheseg_nota veredallovio_nota arbol_nota ordentrans"
* You can also specify labels. Be shure of keeping word connected by underlines
global TTESTLABELS "veredas_limpias espacios_verdes iluminacion seguridad_de_noche veredas_cuando_llueve arbolado orden_transito"
* Define here the name of the binary variable that signals the two groups. In this case is called "intervencion"
gen groups=intervencion

sum $TTESTVARS
/* Define el nombre de la tabla*/
capture: erase descstats.txt

file open fh using descstats.txt, write replace
file write fh _n _tab "Difference in Means Test"
file write fh _n _tab "Variable" _tab "Obs Control" _tab "Media Control" _tab "Obs Tratamiento" _tab "Mean Treatment" _tab "Diff" _tab "t"
local i=1
foreach var of global TTESTVARS {
local etiqueta : word `i’ of $TTESTLABELS
capture quietly ttest `var’, by(groups)
local se_1 = (r(sd_1))/(r(N_1))^0.5
local se_2 = (r(sd_2))/(r(N_2))^0.5
local dif =(r(mu_1)-r(mu_2))

file write fh _n _tab "`etiqueta’" _tab %12.0fc (r(N_1)) _tab %12.3fc (r(mu_1)) _tab %12.0fc (r(N_2)) _tab %12.3fc (r(mu_2)) _tab %12.3fc (`dif’) _tab %12.3fc (r(t))
file write fh _n _tab _tab _tab %12.3fc (`se_1′) _tab _tab %12.3fc (`se_2′) _tab %12.3fc (r(se)) _tab %12.3fc (r(p))
local i=`i’+1
}
file close fh
type descstats.txt
[/sourcecode]