------------------------------------------------------------------------------ log: c:\bill\jpsm\natal95.log log type: text opened on: 4 Nov 2004, 05:48:05 . * use the natality detail data set; . use c:\bill\jpsm\natal95; . * print out variable labels; . desc; Contains data from c:\bill\jpsm\natal95.dta obs: 14,230 vars: 7 27 Oct 2004 14:58 size: 170,760 (98.4% of memory free) ------------------------------------------------------------------------------ > - storage display value variable name type format label variable label ------------------------------------------------------------------------------ > - birthw int %9.0g birth weight in grams smoked byte %9.0g =1 if mom smoked during pregnancy age byte %9.0g moms age at birth married byte %9.0g =1 if married race4 byte %9.0g 1=white,2=black,3=asian,4=other educ5 byte %9.0g 1=0-8, 2=9-11, 3=12, 4=13-15, 5=16+ visits byte %9.0g prenatal visits ------------------------------------------------------------------------------ > - Sorted by: . * construct indicator for low birth weight; . gen lowbw=birthw<=2500; . label variable lowbw "dummy variable, =1 ifBW<2500 grams"; . * get frequencies; . tab lowbw smoked, col row cell; +-------------------+ | Key | |-------------------| | frequency | | row percentage | | column percentage | | cell percentage | +-------------------+ dummy | variable, | =1 | =1 if mom smoked ifBW<2500 | during pregnancy grams | 0 1 | Total -----------+----------------------+---------- 0 | 11,626 1,745 | 13,371 | 86.95 13.05 | 100.00 | 94.64 89.72 | 93.96 | 81.70 12.26 | 93.96 -----------+----------------------+---------- 1 | 659 200 | 859 | 76.72 23.28 | 100.00 | 5.36 10.28 | 6.04 | 4.63 1.41 | 6.04 -----------+----------------------+---------- Total | 12,285 1,945 | 14,230 | 86.33 13.67 | 100.00 | 100.00 100.00 | 100.00 | 86.33 13.67 | 100.00 . * run a logit model; . xi: logit lowbw smoked age married i.educ5 i.race4; i.educ5 _Ieduc5_1-5 (naturally coded; _Ieduc5_1 omitted) i.race4 _Irace4_1-4 (naturally coded; _Irace4_1 omitted) Iteration 0: log likelihood = -3244.039 Iteration 1: log likelihood = -3149.3534 Iteration 2: log likelihood = -3137.0703 Iteration 3: log likelihood = -3136.9913 Iteration 4: log likelihood = -3136.9912 Logit estimates Number of obs = 14230 LR chi2(10) = 214.10 Prob > chi2 = 0.0000 Log likelihood = -3136.9912 Pseudo R2 = 0.0330 ------------------------------------------------------------------------------ lowbw | Coef. Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- smoked | .6740651 .0897869 7.51 0.000 .4980861 .8500441 age | .0080537 .006791 1.19 0.236 -.0052564 .0213638 married | -.3954044 .0882471 -4.48 0.000 -.5683654 -.2224433 _Ieduc5_2 | -.1949335 .1626502 -1.20 0.231 -.5137221 .1238551 _Ieduc5_3 | -.1925099 .1543239 -1.25 0.212 -.4949791 .1099594 _Ieduc5_4 | -.4057382 .1676759 -2.42 0.016 -.7343769 -.0770994 _Ieduc5_5 | -.3569715 .1780322 -2.01 0.045 -.7059081 -.0080349 _Irace4_2 | .7072894 .0875125 8.08 0.000 .5357681 .8788107 _Irace4_3 | .386623 .307062 1.26 0.208 -.2152075 .9884535 _Irace4_4 | .3095536 .2047899 1.51 0.131 -.0918271 .7109344 _cons | -2.755971 .2104916 -13.09 0.000 -3.168527 -2.343415 ------------------------------------------------------------------------------ . * get marginal effects; . mfx compute; Marginal effects after logit y = Pr(lowbw) (predict) = .05465609 ------------------------------------------------------------------------------ variable | dy/dx Std. Err. z P>|z| [ 95% C.I. ] X ---------+-------------------------------------------------------------------- smoked*| .0436744 .00706 6.18 0.000 .029834 .057514 .136683 age | .0004161 .00035 1.19 0.236 -.000271 .001104 26.6564 married*| -.0218806 .0052 -4.21 0.000 -.032074 -.011687 .683204 _Ieduc~2*| -.0095123 .00749 -1.27 0.204 -.024188 .005164 .165495 _Ieduc~3*| -.0096965 .00758 -1.28 0.201 -.024554 .005161 .345397 _Ieduc~4*| -.0190499 .00714 -2.67 0.008 -.033043 -.005057 .22319 _Ieduc~5*| -.0169077 .00771 -2.19 0.028 -.032027 -.001788 .216093 _Irace~2*| .0453844 .00675 6.72 0.000 .032148 .058621 .17168 _Irace~3*| .0236917 .02204 1.07 0.282 -.019506 .06689 .010401 _Irace~4*| .018225 .01363 1.34 0.181 -.008488 .044938 .031694 ------------------------------------------------------------------------------ (*) dy/dx is for discrete change of dummy variable from 0 to 1 . * run a logit but report the odds ratios instead; . xi: logistic lowbw smoked age married i.educ5 i.race4; i.educ5 _Ieduc5_1-5 (naturally coded; _Ieduc5_1 omitted) i.race4 _Irace4_1-4 (naturally coded; _Irace4_1 omitted) Logistic regression Number of obs = 14230 LR chi2(10) = 214.10 Prob > chi2 = 0.0000 Log likelihood = -3136.9912 Pseudo R2 = 0.0330 ------------------------------------------------------------------------------ lowbw | Odds Ratio Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- smoked | 1.962198 .1761796 7.51 0.000 1.645569 2.33975 age | 1.008086 .0068459 1.19 0.236 .9947574 1.021594 married | .6734077 .0594262 -4.48 0.000 .5664506 .8005604 _Ieduc5_2 | .8228894 .1338431 -1.20 0.231 .5982646 1.131852 _Ieduc5_3 | .8248862 .1272996 -1.25 0.212 .6095837 1.116233 _Ieduc5_4 | .6664847 .1117534 -2.42 0.016 .4798043 .9257979 _Ieduc5_5 | .6997924 .1245856 -2.01 0.045 .4936601 .9919973 _Irace4_2 | 2.028485 .1775178 8.08 0.000 1.70876 2.408034 _Irace4_3 | 1.472001 .4519957 1.26 0.208 .8063741 2.687076 _Irace4_4 | 1.362817 .2790911 1.51 0.131 .9122628 2.035893 ------------------------------------------------------------------------------ . log close; log: c:\bill\jpsm\natal95.log log type: text closed on: 4 Nov 2004, 05:48:39 ------------------------------------------------------------------------------