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From |
"Mihai-Andrei Popescu-Greaca" <mischai@gmx.de> |

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

Subject |
AW: AW: st: PSMATCH with 2 conditions |

Date |
Mon, 20 Sep 2010 23:50:46 +0200 |

Dear Judson, Just tried out the multiplication with 10 and 1000 on the nlswork dataset, and again, the T-values are different (without bootstrapping). When I use pscore2 (multiplication with 10) I get a T of 9.16, Difference is .102809747 and SE is .011229545. Using pscore3 (*1000) yields a T of 4.02, a Difference of .092227641 and a SE of .02294341. The only explanation I came up with is that (my) Stata "looses" decimals with each multiplication or performs a "mysterious" round-up. I.e. if my initial pscore is 0.28732124 (like row 3 in the dataset), then the pscore2 is 720.28729 and the pscore3 is 72000.287. IF my theory holds, then by multiplying with a huge number, all decimals should disappear. I generated a pscore4 (*1000000) and now I only see 72000000, but T is still 4.72, Difference is .263281083 and SE .055774089, hence this doesn't make sense either. I'm using Stata 11.1..I really don't know what else can be wrong..:((((( PS: I exported the data to excel, and only the "short" numbers get exported (i.e. 72000.287, and NOT 72*1000+0.287321424) Best, Mihai -----Ursprüngliche Nachricht----- Von: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Caskey, Judson Gesendet: Montag, 20. September 2010 17:48 An: statalist@hsphsun2.harvard.edu Betreff: re: AW: st: PSMATCH with 2 conditions Mihai, I was unable to replicate the problem. Can you try replicating it on one of the public datasets and send an example? Here is what I tried: webuse nlswork logit union collgrad age tenure not_smsa c_city south nev_mar predict pscore if e(sample), pr gen pscore2=year*10+pscore gen pscore3=year*1000+pscore psmatch2 union, pscore(pscore2) outcome(ln_wage) caliper(0.5) psmatch2 union, pscore(pscore3) outcome(ln_wage) caliper(0.5) I get the same results in both of the psmatch2 calls. The issue may be with the bootstrapping procedure rather than with the call to psmatch2, itself. Regards, Judson ---------------------------------- Hi Judson, thanks for the great tip & sorry for the late reply but I've been pretty busy lately. One thing though: My industry is only 2 digit, so if I only want to match by industry, I just multiply industry by 10 and then add the pscore, as follows: gen pscore2=3-digit-industry*10+pscore And then psmatch2 as indicated by you in the link. THE PROBLEM occurred when I used 1000 instead of 10, and then 100000 instead of 1000; ALL 3 yielded different results (T & Z-scores when bootstrapping SEs) Do you have an explanation for the different results?? Regards, Mihai * * 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/ * * 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**:**re: AW: st: PSMATCH with 2 conditions***From:*"Caskey, Judson" <judson.caskey@anderson.ucla.edu>

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