--------------------------------------------------------------------------------------------------- log: C:\mydocs\MPH\Text\SecondEdition\WebDoFiles\2.20.Framingham.log log type: text opened on: 28 Dec 2007, 11:02:12 . * 2.20.Framingham.log . * . * Regression of log systolic blood pressure against log body mass . * index at baseline in men and women from the Framingham Heart Study. . * . use C:\WDDtext\2.20.Framingham.dta, clear . generate logsbp = log(sbp) . generate logbmi = log(bmi) (9 missing values generated) . codebook sex ------------------------------------------------------------------------------------------------- sex Sex ------------------------------------------------------------------------------------------------- type: numeric (float) label: sex range: [1,2] units: 1 unique values: 2 missing .: 0/4699 tabulation: Freq. Numeric Label 2049 1 Men 2650 2 Women . regress logsbp logbmi if sex==1 Source | SS df MS Number of obs = 2047 -------------+------------------------------ F( 1, 2045) = 137.93 Model | 2.5901294 1 2.5901294 Prob > F = 0.0000 Residual | 38.4025957 2045 .018778775 R-squared = 0.0632 -------------+------------------------------ Adj R-squared = 0.0627 Total | 40.9927251 2046 .020035545 Root MSE = .13704 ------------------------------------------------------------------------------ logsbp | Coef. Std. Err. t P>|t| [95% Conf. Interval] -------------+---------------------------------------------------------------- logbmi | .272646 .0232152 11.74 0.000 .2271182 .3181739 _cons | 3.988043 .0754584 52.85 0.000 3.84006 4.136026 ------------------------------------------------------------------------------ . predict yhatmen, xb (9 missing values generated) . regress logsbp logbmi if sex==2 Source | SS df MS Number of obs = 2643 -------------+------------------------------ F( 1, 2641) = 461.90 Model | 12.0632111 1 12.0632111 Prob > F = 0.0000 Residual | 68.9743032 2641 .026116737 R-squared = 0.1489 -------------+------------------------------ Adj R-squared = 0.1485 Total | 81.0375143 2642 .030672791 Root MSE = .16161 ------------------------------------------------------------------------------ logsbp | Coef. Std. Err. t P>|t| [95% Conf. Interval] -------------+---------------------------------------------------------------- logbmi | .3985947 .0185464 21.49 0.000 .3622278 .4349616 _cons | 3.593017 .0597887 60.10 0.000 3.475779 3.710254 ------------------------------------------------------------------------------ . predict yhatwom, xb (9 missing values generated) . sort logbmi . * . * Scatter plots of SBP by BMI for men and women. The estimated . * expected SBP is shown for each gender on these plots. The . * expected SBP is shown for both genders on the male scatter . * plot. Both SBP and BMI are plotted on a log scale. . * . scatter logsbp logbmi , color(gray) symbol(Oh) /// > || line yhatmen logbmi if sex == 1, lwidth(medthick) /// > || line yhatwom logbmi, lwidth(medthick) lpattern(dash) /// > , by(sex, legend(off)) ytitle(Systolic Blood Pressure) /// > xsize(8) ylabel( 4.61 "100" 5.01 "150" 5.3 "200" /// > 5.52 "250") ymtick(4.38 4.5 4.7 4.79 4.87 4.94 5.08 /// > 5.14 5.19 5.25 5.35 5.39 5.43 5.48 5.56 5.60) /// > xtitle(Body Mass Index) xlabel( 2.71 "15" 3.22 "25" /// > 3.56 "35" 3.81 "45" 4.01 "55") /// > xmtick(3.0 3.22 3.4 3.56 3.69 3.91 4.01 4.09) . more . scalar s2 = (.018778775*2045 + 0.026116737*2641)/(2047 + 2643-4) . scalar varb_dif = /// > s2*(0.0232152^2/0.018778775 +0.0185464^2/0.026116737) . scalar t = (0.272646 - 0.3985947 )/sqrt( varb_dif) . scalar ci95_lb = (0.272646 - 0.3985947 ) - /// > invttail(4686,.025)*sqrt( varb_dif) . scalar ci95_ub = (0.272646 - 0.3985947 ) + /// > invttail(4686,.025)*sqrt( varb_dif) . display "s2 = " s2 ", varb_dif = " varb_dif ", t = " t s2 = .0229144, varb_dif = .00095943, t = -4.0661848 . display "ci95_lb = " ci95_lb ", ci95_ub = " ci95_ub ci95_lb = -.18667361, ci95_ub = -.06522379 . display 2*ttail(4686,abs(t)) .00004857 . log close log: C:\mydocs\MPH\Text\SecondEdition\WebDoFiles\2.20.Framingham.log log type: text closed on: 28 Dec 2007, 11:03:19 -------------------------------------------------------------------------------------------------