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From |
john metcalfe <johnzmetcalfe@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: nlcom question |

Date |
Wed, 3 Mar 2010 19:31:24 -0800 |

Dear Statalist, I have a simple question I hope someone can help me with. I am using OLS with robust variance estimators to model a continuous, log-transformed DV ranging from 0 to 10 in increments of 0.01 (this is an immunologic test in common use in the U.S.). My goal is to determine whether or not there are differences in this test performance according to a categorical independent variable (rax, 4 levels) with an interaction term (nt, 3 levels) and other categorical covariates, as below: Linear regression Number of obs = 2734 F( 17, 1716) = 133.04 Prob > F = 0.0000 R-squared = 0.4007 Root MSE = 1.6254 ------------------------------------------------------------------------------ | Robust ln_ag | Coef. Std. Err. t P>|t| [95% Conf. Interval] -------------+---------------------------------------------------------------- _Irax_1 | -.3175203 .1598442 -1.99 0.047 -.6310302 -.0040104 _Irax_2 | -.5266611 .22524 -2.34 0.019 -.968435 -.0848873 _Irax_3 | -.0842108 .1791368 -0.47 0.638 -.4355602 .2671386 _Int_1 | 3.201428 .1158472 27.63 0.000 2.974212 3.428645 _Int_2 | 2.228758 .1441987 15.46 0.000 1.945934 2.511582 _IraxXnt~1_1 | .05004 .2237556 0.22 0.823 -.3888224 .4889025 _IraxXnt~1_2 | 1.110956 .4651867 2.39 0.017 .1985636 2.023349 _IraxXnt~2_1 | 1.094455 .2752091 3.98 0.000 .5546741 1.634236 _IraxXnt~2_2 | 1.225901 .4853438 2.53 0.012 .273973 2.177829 _IraxXnt~3_1 | .5545474 .2237545 2.48 0.013 .1156871 .9934077 _IraxXnt~3_2 | 1.250381 .3833228 3.26 0.001 .4985518 2.00221 age_cntr | .0047114 .0028156 1.67 0.094 -.0008109 .0102338 female | -.1865305 .0811696 -2.30 0.022 -.3457323 -.0273287 jka1 | -.3056762 .0994589 -3.07 0.002 -.5007496 -.1106027 jka2 | -.3657116 .1416161 -2.58 0.010 -.64347 -.0879533 prevt | .3526168 .1933732 1.82 0.068 -.0266552 .7318889 dm | .3199483 .1509238 2.12 0.034 .0239343 .6159623 _cons | -3.02986 .1154191 -26.25 0.000 -3.256237 -2.803483 ------------------------------------------------------------------------------ To estimate the difference in the backtransformed DV between rax3 and rax0, I am using: scalar rmse = e(rmse) nlcom exp(_b[_cons]+_b[_Irax_3] + _b[_Int_2] + _b[_IraxXnt_3_2] +rmse^2/2)-exp(_b[_cons] + _b[_Int_2] + rmse^2/2), but I think I need to also add in the coefficients for the other predictors, multiplied by the average value of the covariate in both sides of the nlcom statement. Is there an easy way to go about doing this? Thanks in advance, John * * 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/

**Follow-Ups**:**Re: st: nlcom question***From:*Stas Kolenikov <skolenik@gmail.com>

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