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6 messages · Dongli Zhou, Marc Schwartz, Liaw, Andy

Marc Schwartz
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On Nov 14, 2011, at 4:11 PM, Dongli Zhou wrote:

            

      
      
      
    

        
Hi,

Presuming that you are using the nBinomial() function, see the 'ratio' argument, which defines the desired sample size ratio between the two groups.

See ?nBinomial and the examples there, which does include one using the 'ratio' argument.

HTH,

Marc Schwartz

  
  


  


      

    

    

      
      

        


  

        

      Dongli Zhou
    

    

      
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Hi, Marc,

Thank you very much for the reply. I'm using the gsDesign function to create an object of type gsDesign. But the inputs do not include the 'ratio' argument.

Dongli

        
On Nov 14, 2011, at 5:50 PM, Marc Schwartz <marc_schwartz at me.com> wrote:

        

            

      
      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Liaw, Andy
    

    

      
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Hi Dongli,

Questions about usage of specific contributed packages are best directed toward the package maintainer/author first, as they are likely the best sources of information, and they don't necessarily subscribe to or keep up with the daily deluge of R-help messages.

(In this particular case, I'm quite sure the package maintainer for gsDesign doesn't keep up with R-help.)

Best,
Andy

            

      
      
      
    

        

      
      
    

        
Notice:  This e-mail message, together with any attachme...{{dropped:11}}

  
  


  


      

    

    

      
      

        


  

        

      Marc Schwartz
    

    

      
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Hi Dongli,

Sorry for the delay in following up.

You might want to read the dsDesignManual.pdf document, which is available in the 'inst/doc' folder in the package source tarball on CRAN, or in the package 'doc' directory in your R installation. Use:

  system.file(package = "gsDesign")

to get the package top directory for your installation. The above file will be in the 'doc' sub-directory from there. It has more extensive worked examples than the default package manual.


Simple non-inferiority example from ?nBinomial, with 2:1 ratio:

n.Fix <- nBinomial(p1 = .677, p2 = .677, delta0 = 0.07, ratio = 2)

            

      
      
      
    

        
[1] 2056.671

# Adjust that *up* to an integer multiple of 3
n.Fix <- 2058


# Change 'outtype' to 2 if you want to see per arm sample sizes
# eg:

            

      
      
      
    

        
$n1
[1] 685.5569

$n2
[1] 1371.114




# Simple default GS design using the fixed study design sample size from above, 
# which is not yet adjusted for interim analyses

            

      
      
      
    

        
Asymmetric two-sided group sequential design with
90 % power and 2.5 % Type I Error.
Upper bound spending computations assume
trial continues if lower bound is crossed.

                  ----Lower bounds----  ----Upper bounds-----
  Analysis   N    Z   Nominal p Spend+  Z   Nominal p Spend++
         1  734 -0.24    0.4057 0.0148 3.01    0.0013  0.0013
         2 1468  0.94    0.8267 0.0289 2.55    0.0054  0.0049
         3 2202  2.00    0.9772 0.0563 2.00    0.0228  0.0188
     Total                      0.1000                 0.0250 
+ lower bound beta spending (under H1):
 Hwang-Shih-DeCani spending function with gamma = -2
++ alpha spending:
 Hwang-Shih-DeCani spending function with gamma = -4

Boundary crossing probabilities and expected sample size
assume any cross stops the trial

Upper boundary (power or Type I Error)
          Analysis
   Theta      1      2      3  Total   E{N}
  0.0000 0.0013 0.0049 0.0171 0.0233 1286.0
  0.0715 0.1412 0.4403 0.3185 0.9000 1628.4

Lower boundary (futility or Type II Error)
          Analysis
   Theta      1      2      3  Total
  0.0000 0.4057 0.4290 0.1420 0.9767
  0.0715 0.0148 0.0289 0.0563 0.1000


So rather than needing 2058 from the fixed design, you actually need 2202 (1468 in one arm and 734 in the other).

I would urge you to read the manual I reference above and as Andy has noted in his reply, contact Keaven directly for further assistance with this package.

HTH,

Marc

        
On Nov 14, 2011, at 5:13 PM, Dongli Zhou wrote:

        

            

      
      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Dongli Zhou
    

    

      
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Thank you so much for the help! It is really appreciated!

Dongli

        
On Nov 15, 2011, at 9:19 AM, Marc Schwartz <marc_schwartz at me.com> wrote: