[U] User's Guide

268 [ U ] 20 Estimation and postestimation commands. regress mpg weight 5.rep78 if foreignSource SS df MS Number of obs = 21F( 2, 18) = 10.21Model 423.317154 2 211.658577 Prob > F = 0.0011Residual 372.96856 18 20.7204756 R-squared = 0.5316Adj R-squared = 0.4796Total 796.285714 20 39.8142857 Root MSE = 4.552mpg Coef. Std. Err. t P>|t| [95% Conf. Interval]weight -.0131402 .0029684 -4.43 0.000 -.0193765 -.00690385.rep78 5.052676 2.13492 2.37 0.029 .5673764 9.537977_cons 52.86088 6.540147 8.08 0.000 39.12054 66.60122. summarize mpg weight 5.rep78 if e(sample)Variable Obs Mean Std. Dev. Min Maxmpg 21 25.28571 6.309856 17 41weight 21 2263.333 364.7099 1760 31705.rep78 21 .4285714 .5070926 0 1Twenty-one observations were used in the above regression and we subsequently obtained the meansfor those same 21 observations by typing summarize . . . if e(sample). There are two reasonsobservations were dropped: we specified if foreign when we ran the regression, and there wereobservations for which 5.rep78 was missing. The reason does not matter; e(sample) is true if theobservation was used and false otherwise.You can use if e(sample) on the end of any Stata command that allows an if exp.Here Stata has a shorthand command that produces the same results as summarize . . . ife(sample):. estat summarize, labelEstimation sample regress Number of obs = 21Variable Mean Std. Dev. Min Max Labelmpg 25.28571 6.309856 17 41 Mileage (mpg)weight 2263.333 364.7099 1760 3170 Weight (lbs.)5.rep78 .4285714 .5070926 0 1 Repair Record 1978See [R] estat.20.7 Specifying the width of confidence intervalsYou can specify the width of the confidence intervals for the coefficients using the level() optionat estimation or when you play back the results.