Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[no subject]
Good luck,
Adam Olszewski
On Sat, Jan 12, 2013 at 7:37 AM, simone ferro <[email protected]> wrote:
> dear Statalist,
>
> I would please need some clarifications about the interpretation of the command pstest after running psmatch2:
> I report a random output just as an example.
>
> pstest ebitda_marg asset employees av_age donne_perc laureati_perc bluecollar_perc, both
>
> ------------------------------------------------------------------------------
> Unmatched | Mean %reduct | t-test
> Variable Matched | Treated Control %bias |bias| | t p>|t|
> --------------------------+----------------------------------+----------------
> ebitda_marg Unmatched | 11.404 8.2304 36.8 | 3.25 0.001
> Matched | 10.746 10.555 2.2 94.0 | -2.33 0.020
> | |
> asset Unmatched | 395.52 34.389 28.6 | 2.48 0.014
> Matched | 115.36 89.157 2.1 92.7 | -2.10 0.037
> | |
> employees Unmatched | 641.98 508.48 4.6 | 0.42 0.677
> Matched | 474.12 704.43 -8.0 -72.5 | 0.18 0.857
> | |
> av_age Unmatched | 53.369 56.714 -45.0 | -4.06 0.000
> Matched | 53.39 53.051 4.6 89.9 | 3.84 0.000
> | |
> donne_perc Unmatched | .34711 .37372 -11.8 | -1.06 0.291
> Matched | .34805 .33374 6.3 46.2 | 0.16 0.874
> | |
> laureati_perc Unmatched | .26656 .18165 35.4 | 3.15 0.002
> Matched | .26815 .23665 13.2 62.9 | -1.52 0.129
> | |
> bluecollar_~c Unmatched | .30019 .3349 -11.2 | -1.00 0.317
> Matched | .30425 .33592 -10.2 8.7 | -0.28 0.776
> | |
> ------------------------------------------------------------------------------
> If I understood well, reported t-.tests' null hypothesis is that the two covariates are equal in treated and control group,
> so I should look at t-tests to check if the groups are well balanced,
> In some tutorial instead I've read that the right approach is to look at the bias percentage that should be under 10 to be considered ok,
>
> Which one of the two approaches is the right one?it's fundamental for me to understand because they provide totally different interpretations.
> indeed if I look at t-tests, I find problems with ebitda_margin, asset and av_age, because they are significantly different in the two groups,
> while if I look at the bias percentage, I find problem with laureati_perc and blecollar, because their bias% are bigger than 10.
>
> I also would appreciate your confirmation of the interpretation of the two indicators(%bias and t-tests), because with this interpretation I find the two values contradictory.
> looking for example at the variable av_age, I find a very little bias, and the means after matching of treated and control group are almost identical(53.39 and 53.051), by the way the t-test reports a p-value of 0.000!
> So it seems like I have misunderstood the meaning of the t.test because I don't think that 53.39 and 53.051 can be statistically different with a t-stat of 3.84, also given the nature of the variable(the average age of the managers of a firm) that should infact be quite variable.
> The same happens with the variable ebitda, which reports a bias% of 2.2% and almost identical values(10.746 and 10.555), but t-stat is -2.33 and p-value 2%!
> Can you please help me?
> thanks in advance for the help,
> Regards,
> Simone Ferro
> *
> * 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/
*
* 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/