quietly {
  /*
     Cook's D tests to see whether the error in the model changes 
       when a specific data value is either included, or excluded 
       from the model.

     Cook's Distance for the i-th observation is based on the 
       differences between the predicted responses from the model 
       constructed from all of the data and the predicted responses 
       from the model constructed by setting the i-th observation 
       aside. 

     Cook's D differs from DFITS by looking at the effect on ALL
       the predicted values, not just the i-th.

     There are only informal guidelines for interpreting Cook's D.
       1. One recommendation is to consider values to be large 
           which exceed 4/(n-j-1). (j=number of IV's)
       2. Another suggested rule is to consider any value greater 
           than 1 or 2 as indicating that an observation requires 
           a careful look.
       3. Finally, some researchers look for gaps between the D values. 
  */

  regress  y  x 
  predict  y_cook , cooksd

  regress y1  x 
  predict y1_cook , cooksd

  regress y2  x 
  predict y2_cook , cooksd

  local j=1
  local n=10
  local cookscrit1= 4/(`n'-`j'-1)
  local cookscrit2= `cookscrit1'*-1
  local cookscrit = round(`cookscrit1',.001)

  #delimit ;
  graph twoway (scatter  y_cook obs),
    title("Original Data")
    xlabel(1(1)10)
    ylabel(-1(1)1) ytick(-1(.2)1.4)
    yline(`cookscrit1', lp(dash) lw(thick))
    yline(`cookscrit2', lp(dash) lw(thick))
    name(cooks1, replace) nodraw
  ;
  #delimit cr

  #delimit ;
  graph twoway (scatter y1_cook obs),
    title("Scenario #1")
    xlabel(1(1)10)
    ylabel(-1(1)1) ytick(-1(.2)1.4)
    yline(`cookscrit1', lp(dash) lw(thick))
    yline(`cookscrit2', lp(dash) lw(thick))
    name(cooks2, replace) nodraw
  ;
  #delimit cr

  #delimit ;
  graph twoway (scatter y2_cook obs),
    title("Scenario #2")
    xlabel(1(1)10)
    ylabel(-1(1)1) ytick(-1(.2)1.4)
    yline(`cookscrit1', lp(dash) lw(thick))
    yline(`cookscrit2', lp(dash) lw(thick))
    name(cooks3, replace) nodraw
  ;
  #delimit cr

  #delimit ;
  graph combine cooks1 cooks2 cooks3,
    title("Plot of Cook's D")
    note("|Cook's D| > `cookscrit'")
    name(cooksd, replace)
  ;
  #delimit cr

  drop y_cook-y2_cook
}