*! version 1.0.0  Hilbe  Oct-12-92  STB-11 sg15
* Sample Size calculation:  Means & proportions 
program define sampsiz
   version 3.0
   parse "`*'", parse(" ,")
   local alpha "`1'"
   local power "`2'"
   local nullh "`3'"
   local testh "`4'" 
   if "`testh'"=="" {
        di in red _n "Input is as follows:"
        di in red "sampsiz alpha power null test, [pr|m] t([p|c]) s([1|2]) <sd> <sd1> <sd2> <r()>"
        di in red _n "alpha     usually .01, .05, .1"
        di in red    "power =   1-beta (usually 4 times alpha:.01~.95,.05~.80)" 
        di in red    "null  =   null mean or proportion"
        di in red    "test  =   test or alternate mean or proportion"
        di in red    "[pr|m]    REQUIRED : pr=proportion, m=means"
        di in red    "t([p|c])  REQUIRED : p =population, c=comparison" 
        di in red    "s([1|2])  default=2: use s(1) for 1-sided test"
        di in red    "sd      = use only for means-population tests"
        di in red    "sd1 sd2 = use only for means-comparison tests"
        di in red    "r()     = rate or multiple for unequal sample size comparison tests"
        exit 100
   }
   conf  n `alpha'
   conf  n `power'
   conf  n `nullh'
   conf  n `testh'
   mac shift
   mac shift
   mac shift
   mac shift
   local options "Sides(integer 2) PRop Mean Type(string) Rate(real 1.0) SD(real 1.0) SD1(real 1.0) SD2(real 1.0)"
   parse "`*'"

   if "`sides'"=="1" {
        local alphaz = invnorm(1- `alpha')   
        local powerz = invnorm(`power')
   }
   else {
        local alphaz = invnorm(1- `alpha'/2)   
        local powerz = invnorm(`power')
   }
           
  if "`prop'"!="" {

  if "`type'"=="p" {
           #delimit ;
           local sizen = (`alphaz'*sqrt((`nullh'*(1-`nullh')))) +
                         (`powerz'*sqrt((`testh'*(1-`testh'))));
           local sized = abs(`nullh'-`testh');
           local size  = (`sizen'/`sized')^2;
           #delimit cr
   }
   if "`type'"=="c" {
           #delimit ;
           local meanp  = (`nullh'+(`rate'*`testh'))/(`rate'+1);
           local meanq  = 1- `meanp';
           local sizen1 = `alphaz'*sqrt((`rate'+1)*`meanp'*`meanq'); 
           local sizen2 = sqrt(`rate'*`nullh'*(1-`nullh')+`testh'* (1-`testh'));
           local sizen3 = `powerz'*`sizen2';
           local sizen4 = (`sizen1' + `sizen3')^2;   /* - */
*           local sized = `rate'* (`nullh'-`testh')^2; 
           local sized = `rate'* (abs(`nullh'-`testh'))^2;
           local size  = `sizen4'/`sized';
           local size  = (`size'/4) * ((1+ sqrt(1+(2*(`rate'+1)) /
                         (`size'* `rate'* abs(`testh'-`nullh')))))^2;
           #delimit cr
   }

   di in gr _n(2) _col(20) "Estimated Sample Size Computation"    
   di in gr       _col(30) "Proportions"
   if "`type'"=="c" {
    di in gr _n " Number of cases: Sample 1 => " in ye int(`size'+.5)
    di in gr    " Number of cases: Sample 2 => " in ye int((`size'+.5)*`rate')
    di in gr    " Z-alpha                   => " in ye %3.2f `alphaz'
    di in gr    " Z-power                   => " in ye %3.2f `powerz'
   }
   else  {
    di in gr _n " Number of cases => " in ye int(`size'+.5)
    di in gr " Z-alpha         => " in ye %3.2f `alphaz'
    di in gr " Z-power         => " in ye %3.2f `powerz'
   }
  }
  if "`mean'"!=""  {

  if "`type'"=="p" {
          local size = (((`alphaz'+`powerz')*`sd')/(`testh'-`nullh'))^2
          di in gr _n(2) _col(20) "Estimated Sample Size Computation"    
          di in gr       _col(33) "Means"
          di in gr _n " Number of cases => " in ye int(`size'+.5)
          di in gr " Z-alpha         => " in ye %3.2f `alphaz'
          di in gr " Z-power         => " in ye %3.2f `powerz'
  }

  if "`type'"=="c" {
          #delimit ;
          local sizen1 = (`sd1'^2+(`sd2'^2*`rate'))*(`alphaz'+`powerz')^2;
          local sized1 = (`testh'-`nullh')^2;
          local size1  = `sizen1'/`sized1';
*          local sizen2 = ((`rate'*`sd1'^2)+`sd2'^2)*(`alphaz'+`powerz')^2;
*          local sized2 = (`testh'-`nullh')^2;
*          local size2  = `sizen2'/`sized2';
          local size2  = `size1'/`rate';
          #delimit cr
          di in gr _n(2) _col(20) "Estimated Sample Size Computation"    
          di in gr       _col(33) "Means" 
          di in gr _n " Number of cases: Sample 1 => " in ye int(`size1'+.5)
          di in gr    "                  Sample 2 => " in ye int(`size2'+.5) 
          di in gr    " Z-alpha                   => " in ye %3.2f `alphaz'
          di in gr    " Z-power                   => " in ye %3.2f `powerz'
   }

          
}
end