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Date:         Mon, 15 Aug 2011 09:39:53 -0700
Reply-To:     Steve Denham <stevedrd@yahoo.com>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Steve Denham <stevedrd@YAHOO.COM>
Subject:      Re: Proc plan
Comments: To: William Shakespeare <shakespeare_1040@HOTMAIL.COM>
In-Reply-To:  <201108151551.p7FAl9Fw006452@willow.cc.uga.edu>
Content-Type: text/plain; charset=iso-8859-1

I don't see a need to include "block" as a fixed effect.  The following should be adequate:   proc mixed; class tx block; model y=tx ; random intercept/subject=block; I prefer the subject= form of the random statement, so that I can flip easily to:   proc glimmix method=quad; class tx block; model y=tx; random intercept/subject=block;   Good luck! Steve Denham Associate Director, Biostatistics MPI Research, Inc. From: William Shakespeare <shakespeare_1040@HOTMAIL.COM> >To: SAS-L@LISTSERV.UGA.EDU >Sent: Monday, August 15, 2011 11:51 AM >Subject: Re: Proc plan > >On Sat, 13 Aug 2011 15:54:24 -0400, William Shakespeare ><shakespeare_1040@HOTMAIL.COM> wrote: > >>I'm reading this article on proc plan >>(http://www.lexjansen.com/pharmasug/2007/ad/ad07.pdf).  The authors >>postulate a 3 treatment arm study with 300 subjects.  This is their >>explanation and the proc plan to make assignments in a permuted block >>randomization: >> >>"Consider the previous example (section 2.1) with three treatments and >>sample size 300. If the block size is 6 then there are 90 >>possible permutations in which each of three treatments can appear with >>equal number of time (i.e. twice)." >> >>6 things taken 3 at a time is 120 permutations, but when you restrict it >>to those with a maximum of 2 repetitions of any treatment it lowers the >>count to 90.  I can't for the life of me remember how this is computed. >>Can anyone refresh my memory? >> >>Also, if one uses all 90 permutations then 540 subjects would have to be >>randomized.  Since the present study only uses 300 doesn't that leave the >>possibility that the reprenstation of some pairs, for example, might be >>unbalanced, e.g. the permutations utilized might have treatment sequence >1- >>2 more often than sequence 2-3.  Is this not generally considered to be >>undesirable in clinical trials? > >Another thing I'm trying to confirm is the proper proc mixed code to >analyze this design (3 treatments with a permuted block randomization, all >at a single location).  I'm thinking: > >proc mixed; >class tx block; >model y=tx block; >random block; > >but I'm not usre it's correct.  And I still can't figure out how the >authors of the paper figured 90 permutations and whether it matters if all >are used in the trial. > > >


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