[Stata Program]

use http://www.gseis.ucla.edu/courses/data/surg335

summarize
correlate
regress y x1 x2 x3 x4
predict p1
predict r1, residual
plot y x1 
plot y x2
plot y x3
plot y x4
plot r1 x1
plot r1 x2
plot r1 x3
plot r1 x4
plot r1 p1
regress logy x1 x2 x3 x4
predict p2
predict r2, residual
plot logy x1 
plot logy x2
plot logy x3
plot logy x4
plot r2 x1
plot r2 x2
plot r2 x3
plot r2 x4
plot r2 p2

[Stata Output]

summarize

Variable |     Obs        Mean   Std. Dev.       Min        Max
---------+-----------------------------------------------------
    case |      54        27.5   15.73213          1         54  
      x1 |      54    5.783333   1.603034        2.6       11.2  
      x2 |      54    63.24074   16.90253          8         96  
      x3 |      54    77.11111   21.25378         23        119  
      x4 |      54    2.744259   1.070356        .74        6.4  
       y |      54    197.1667   145.2994         34        830  
    logy |      54    2.206144   .2737845     1.5315     2.9191  

correlate

(obs=54)

         |     case       x1       x2       x3       x4        y     logy
---------+---------------------------------------------------------------
    case |   1.0000
      x1 |  -0.0981   1.0000
      x2 |   0.0281   0.0901   1.0000
      x3 |   0.1149  -0.1496  -0.0236   1.0000
      x4 |   0.0616   0.5024   0.3690   0.4164   1.0000
       y |  -0.0085   0.3725   0.5540   0.5802   0.7223   1.0000
    logy |   0.0696   0.3464   0.5929   0.6651   0.7262   0.9131   1.0000


regress y x1 x2 x3 x4

  Source |       SS       df       MS                  Number of obs =      54
---------+------------------------------               F(  4,    49) =   62.79
   Model |  936264.538     4  234066.135               Prob > F      =  0.0000
Residual |  182666.962    49  3727.89718               R-squared     =  0.8367
---------+------------------------------               Adj R-squared =  0.8234
   Total |  1118931.50    53  21111.9151               Root MSE      =  61.057

------------------------------------------------------------------------------
       y |      Coef.   Std. Err.       t     P>|t|       [95% Conf. Interval]
---------+--------------------------------------------------------------------
      x1 |   33.16383   7.017275      4.726   0.000       19.06209    47.26557
      x2 |    4.27186   .5633845      7.582   0.000       3.139696    5.404023
      x3 |   4.125738   .5111609      8.071   0.000       3.098522    5.152955
      x4 |   14.09156   12.52533      1.125   0.266      -11.07902    39.26215
   _cons |  -621.5975   64.80043     -9.592   0.000      -751.8189   -491.3762
------------------------------------------------------------------------------

predict p1

(option xb assumed; fitted values)

predict r1, residual

plot y x1 

     830 +  
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         |      *             ** **    * *      *
         | *    *  *   *   * * *  *    **
         |                  ****  * *   *
      34 +     *  **          *          *              *
          +----------------------------------------------------------------+
              2.6              blood clotting score                  11.2


plot y x2

     830 +  
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         | *                      *        * *   *   **    * *   * *
         |                      *     * *  *   **         *        *
      34 +              **           *    * *      *
          +----------------------------------------------------------------+
                8                prognostic index                      96


plot y x3

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    m    |                                                    *
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         |                         *    *        *  **   *   *
         |            *   *    *            * ** * * **                    *
         |    *        *             * *  *** *
      34 + *           **        *     * *                   *
          +----------------------------------------------------------------+
               23              enzyme function test                   119


plot y x4

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         |         *        * ***   *    *
         |     **      ***    **  * *     *
         |        *  * ***      * * *     *
      34 + *     *  *  *  *    * *
          +----------------------------------------------------------------+
              .74               liver function test                    6.4


plot r1 x1

 323.153 +  
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         |               *     *  * *  **                *
         |      *  **       **** **   ****    *          *
         | *       *              *     *    *  *
-80.5226 +                          *
          +----------------------------------------------------------------+
              2.6              blood clotting score                  11.2


plot r1 x2

 323.153 +  
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         |                        *       **  * ***  **    * *  * *
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-80.5226 +                                           *
          +----------------------------------------------------------------+
                8                prognostic index                      96


plot r1 x3

 323.153 +  
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         |                *              * ** ** * ****  *   ** *
         |                              *    * *     *    *
-80.5226 +                                               *
          +----------------------------------------------------------------+
               23              enzyme function test                   119


plot r1 x4

 323.153 +  
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         |         *   **  *** ** *** *   *      *    *
         |               *   *    *      **
-80.5226 +                    *
          +----------------------------------------------------------------+
              .74               liver function test                    6.4


plot r1 p1

 323.153 +  
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         |                    **  *   *             **  *              *
         |                       * *** ** *****   *     *
         |                           *  *  *  ***
-80.5226 +                                       *
          +----------------------------------------------------------------+
         -90.0293                  Fitted values                   524.587


regress logy x1 x2 x3 x4

  Source |       SS       df       MS                  Number of obs =      54
---------+------------------------------               F(  4,    49) =  431.10
   Model |  3.86300182     4  .965750454               Prob > F      =  0.0000
Residual |  .109770615    49  .002240217               R-squared     =  0.9724
---------+------------------------------               Adj R-squared =  0.9701
   Total |  3.97277243    53   .07495797               Root MSE      =  .04733

------------------------------------------------------------------------------
    logy |      Coef.   Std. Err.       t     P>|t|       [95% Conf. Interval]
---------+--------------------------------------------------------------------
      x1 |   .0685202   .0054398     12.596   0.000       .0575885    .0794518
      x2 |   .0092541   .0004367     21.189   0.000       .0083765    .0101318
      x3 |   .0094745   .0003963     23.910   0.000       .0086782    .0102708
      x4 |   .0019254   .0097096      0.198   0.844      -.0175868    .0214376
   _cons |   .4887559   .0502332      9.730   0.000       .3878085    .5897033
------------------------------------------------------------------------------

predict p2

(option xb assumed; fitted values)

predict r2, residual

plot logy x1 

  2.9191 +  
    l    |                        *
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  1.5315 +         *
          +----------------------------------------------------------------+
              2.6              blood clotting score                  11.2


plot logy x2

  2.9191 +  
    l    |                                                                 *
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  1.5315 +                                *
          +----------------------------------------------------------------+
                8                prognostic index                      96


plot logy x3

  2.9191 +  
    l    |                                                             *
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  1.5315 +             *
          +----------------------------------------------------------------+
               23              enzyme function test                   119


plot logy x4

  2.9191 +  
    l    |                                     *
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  1.5315 +          *
          +----------------------------------------------------------------+
              .74               liver function test                    6.4


plot r2 x1

 .139377 +  
         |      *
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    s    |                    *   * *   **       *
         |      *  *
         |         *                                     *
         |        *
         |     *   *                                                       *
         |  
-.100449 + *                        *
          +----------------------------------------------------------------+
              2.6              blood clotting score                  11.2


plot r2 x2

 .139377 +  
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    s    |                      * *       ***       *              *
         |                                                  **
         |                                            *            *
         |               *
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-.100449 +                                           *     *
          +----------------------------------------------------------------+
                8                prognostic index                      96


plot r2 x3

 .139377 +  
         |                     *
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    R    |                                                                 *
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         |                                               **
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-.100449 +                                           *   *
          +----------------------------------------------------------------+
               23              enzyme function test                   119


plot r2 x4

 .139377 +  
         |     *
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    s    |        *    *         ** *              *
         |         *         *
         |                     *                                           *
         |       *
         | *        *                                            *
         |  
-.100449 +               *    *
          +----------------------------------------------------------------+
              .74               liver function test                    6.4


plot r2 p2

 .139377 +  
         |                    *
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    R    |                    *
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    l    |                *   **  **    * * *  *        *
    s    |            *  * **    *  *                              *
         |                                     **
         |                            *                             *
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         | *              *                                             *
         |  
-.100449 +                             *           *
          +----------------------------------------------------------------+
          1.60568                  Fitted values                   2.86227