quietly {
  /* 
     DFBETAS are similar to DFITS. Instead of looking at the 
       difference in fitted value when the i-th observation 
       is included or exlcuded, DFBETAS looks at the change 
       in each regression coefficient.     

     The DFBETAs are standardized so we might be interested in 
       values exceeding 2.  But, in large samples this may
       underestimate changes in the regression coefficients
       due to deletion.

     Beleley et al. (1990) suggest a cutoff of 2/(n^.5)
  */
     
  regress  y  x 
  dfbeta
  rename DFx dfbeta1

  regress y1  x 
  dfbeta
  rename DFx dfbeta2

  regress y2  x 
  dfbeta
  rename DFx dfbeta3

  local n=10
  local dfbetap=2/(`n'^.5)
  local dfbetam=`dfbetap'*-1
  local dfbetacrit=round(`dfbetap',.001)
  noisily di _n "dfbeta critical=" %5.3f `dfbetacrit'

  format dfbeta1 dfbeta2 dfbeta3 %9.4f
  noisily list x y dfbeta1 y1 dfbeta2 y2 dfbeta3, noobs divider
  format dfbeta1 dfbeta2 dfbeta3 %9.1f

  #delimit ;
  graph twoway (scatter dfbeta1 obs),
    ylabel(-.7(.2).7)
    xlabel(1(1)10)
    title("Original Data")
    yline(`dfbetam' 0 `dfbetap', lp(dash) lw(thick))
    ytitle("") xtitle("")
    name(dfbeta1, replace) nodraw
  ;
  #delimit cr

  #delimit ;
  graph twoway (scatter dfbeta2 obs),
    ylabel(-.7(.2).7)
    xlabel(1(1)10)
    title("Scenario #1")
    yline(`dfbetam' 0 `dfbetap', lp(dash) lw(thick))
    ytitle("") xtitle("")
    name(dfbeta2, replace) nodraw
  ;
  #delimit cr

  #delimit ;
  graph twoway (scatter dfbeta3 obs),
    ylabel(-.7(.3)1.9)
    xlabel(1(1)10)
    title("Scenario #2")
    yline(`dfbetam' 0 `dfbetap', lp(dash) lw(thick))
    ytitle("") xtitle("")
    name(dfbeta3, replace) nodraw
  ;
  #delimit cr

  #delimit ;
  graph combine dfbeta1 dfbeta2 dfbeta3,
    title("Plot of DFBETAs")
    note("|DFBETA| > `dfbetacrit'") name(dfbeta, replace)
  ;
  #delimit cr

  drop dfbeta*
}