Random assignment of units to experimental treatments

 

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** Valentim R. Alferes (University of Coimbra, Portugal)
** valferes@fpce.uc.pt

* This syntax job does random assignment of units (subjects) to
* experimental treatments and can be used for Randomized Block
* Designs (Simple or Generalized) and also for Completely Randomized
* Designs with equal n per treatment.

* For Completely Randomized Designs with unequal n per treatment,
* you can use the syntax job posted in:
http://pages.infinit.net/rlevesqu/Syntax/BlockDesign/CRDesigns.txt

* For Randomized Block Designs (Simple), the number of units per block 
* equals the number of treatments (p). The design requires w blocks 
* of p units.

* For the Generalized Randomized Block Designs (see example), the number of
* units per block must be a multiple of the number of treatments (p). The
* design requires w blocks of kp units (k>=2).

* For Completely Randomized Designs with equal n per treatment, you
* must enter number of blocks = 1.

* In the example (Generalized Randomized Block Design) we have:
* 18 subjects (units);
* 3 treatments (p);
* 2 blocks (w);
* 9 subjects per block (9=3p).



DATA LIST FREE /TREAT(A20).
* Enter treatments names (A, B and C in the example).
BEGIN DATA
A B C 
END DATA.
COMPUTE TREATM=$CASENUM.
SAVE OUTFILE=OUTF1.

INPUT PROGRAM.
* Enter number of cases (18 in the example).
LOOP N_CASES=1 TO 18.
* Enter number of treatments (3 in the example).
COMPUTE N_TREATM=3.
* Enter number of blocks (2 in the example).
COMPUTE N_BLOCKS=2.
END CASE.
END LOOP.
END FILE.
END INPUT PROGRAM.

COMPUTE TREATM=MOD($CASENUM,N_TREATM)+1.
SORT CASES BY TREATM (A).
MATCH FILES/FILE=*/TABLE=OUTF1/BY TREATM.
COMPUTE BLOCK=MOD($CASENUM,N_BLOCKS)+1.
SORT CASES BY BLOCK(A) TREAT(A).
SET SEED RANDOM.
COMPUTE RANDOM=RV.UNIFORM(0,1).
SORT CASES BY BLOCK(A) RANDOM(A).
RANK VARIABLES=RANDOM(A) BY BLOCK.
COMPUTE ID=RRANDOM.
FORMATS ID(F8.0) BLOCK(F8.0).
LIST ID BLOCK TREAT.
SORT CASES BY TREAT (A) BLOCK (A) ID (A) .
SPLIT FILE SEPARATE BY TREAT .
LIST BLOCK ID.



* Note 1:
* You can enter any treatment names (up to 20 characters). For example,
* in a Randomized Block Design (Simple) with 10 blocks and 3 treatments:
*    […]
*    BEGIN DATA
*    Treatment_1 Treatment_2 Treatment_3
*    END DATA.
*    […]
*    LOOP N_CASES=1 TO 30.
*    […]
*    COMPUTE N_TREATM=3.
*    […]
*    COMPUTE N_BLOCKS=10.
*    […]



* Note 2:
* Remember to enter N_BLOCKS = 1 in Completely Randomized Designs.
* For example, in a Completely Randomized Factorial Design with 6 treatments, 
* 48 subjects and equal number of subjects per treatment, you have to enter: 
*    […]
*    BEGIN DATA
*    A1B1 A1B2 A2B1 A2B2 A3B1 A3B2
*    END DATA.
*    […]
*    LOOP N_CASES=1 TO 48.
*    […]
*    COMPUTE N_TREATM=6.
*    […]
*    COMPUTE N_BLOCKS=1.
*    […].
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