[gov2001-l] Several matching issues

Hi All, I've got a few matching questions. 1) Does anyone know how to add the "addlvariables" option into the matching summary command? The default is = NULL and I didn't know how to make it

null. I didn't see an example in the MatchIt manual. 2) I was also hoping to hear people's reactions to a curious result in our efforts to find the best balance. First, we did exact matching on age, race, educ, and sex. With age in the equation we lose about half of our observations, but if we take it out, we get this: #Sample sizes: # Control Treated #All 1292 1386 #Matched 1264 1361 #Discarded 28 25 Not bad, but of course, we'd like to have age in the equation, so we

to try nearest neighbor matching. The results of the "balance

outputs suggest that this technique worsened the balance along almost every dimension. Any idea why this would be? Is it worth trying other matching techniques (any particular suggestions)? Percent Balance Improvement: Mean Diff. eQQ Med eQQ Mean eQQ Max distance -27.07 -29.32 -27.494 -173.671 age -19.20 0.00 -15.233 0.000 race -37.39 0.00 -36.585 0.000 educ -24.52 -100.00 -23.777 0.000 sex 64.63 0.00 66.667 0.000 distancexdistance -23.54 -18.54 -23.905 -2.871 distancexage -26.02 -46.51 -26.941 -10.801 distancexrace -24.09 -24.54 -25.474 -17.362 distancexeduc -53.80 -40.59 -52.541 -57.572 distancexsex -29.55 -24.65 -30.105 -36.215 agexage -134.28 -24.84 -14.673 -0.193 agexrace -41.12 -20.00 -39.032 -50.000 agexeduc - 21.88 -15.00 -21.094 -25.000 agexsex 42.65 0.00 -6.838 -16.667 racexrace -40.56 0.00 -39.726 0.000 racexeduc -31.69 -50.00 -30.853 -128.571 racexsex - 33.12 0.00 -31.752 0.000 educxeduc -28.55 -33.33 -27.919 -46.053 educxsex -15.49 0.00 -14.887 0.000 sexxsex 64.63 0.00 66.667 0.000 3) Finally, I don't know if anyone else has encountered this, but if I include the (discard= "hull.both") command in nearest neighbor matching on

dataset about 3000 observations and 24 variables, a desktop computer has insufficient memory to do the calculation (even with the max memory command in R turned on). m.nearest <- matchit(wave1 ~ age+race+educ+sex, data=GSS8504, method="nearest", discard= "hull.both") Many thanks for any suggestions! Best, Abby _______________________________________________ gov2001-l mailing list gov2001-l(a)lists.fas.harvard.edu http://lists.fas.harvard.edu/mailman/listinfo/gov2001-l