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Revision 3 as of 2006-06-30 22:56:57

location: FAQ / CounterBalancing

Counterbalancing for immediate sequential effects

ALGORITHM (Williams)

  1. Write down the N conditions in some order, say {1, 2, 3, ...} and its N-1 cyclic rotations
  2. Apply the interleaving permutation {1, 2, N, 3, N-1,4, N-2, ...} to each of these sequences
  3. If N is even, STOP, otherwise append the N sequences obtained by completely reversing the N sequences generated by steps 1 and 2.

illustrated for N=6 (even)

The interleaving permutation maps {1,2,3,4,5,6} to {1,2,6,3,5,4}.

Applying this to the columns of the cyclic matrix : 

we get the sequentially counterbalanced 6x6 design: 
Illustrated for N=7 (odd) 
The interleaving permutation maps {1,2,3,4,5,6,7} to {1,2,7,3,6,4,5}. 
Applying this to the columns of the cyclic matrix : 
we get the intermediate matrix: 
Appending the mirror image of the intermediate matrix we get the sequentially counterbalanced 14x7 design: 
Here is some MATLAB code to perform this: 
BIBLIOGRAPHY 
Archdeacon, D.S., Dinitz, J.H., and Stinson, D.R. (1980). Some new row­complete Latin Squares. Journal of Combinatorial Theory, Ser. A, 29, 395-- 398. 
Mausumi Bose (Applied Statistics Unit, Indian Statistical Institute Kolkata, India) [http://www.isid.ac.in/~ashish/workshop/mausumiw3.pdf Crossover Designs: Analysis and Optimality Using the Calculus for Factorial Arrangements], Design Workshop Lecture Notes ISI, Kolkata, 25-29 November 2002, 83-192. 
Bradley, J. V. (1958). Complete counterbalancing of immediate sequential effects in a Latin square design, Journal of the American Statistical Association, 53, 525-528. 
Durso, F. T. (1984). A Subroutine for counterbalanced assignment of stimuli to conditions. Behaviour Research Methods, Instruments & Computers, 16(5), 471-472 
Federer, Walter T. and Nguyen, Nam-Ky. [http://designcomputing.net/gendex/pdf/federer.pdf Incomplete block designs]. Volume 2, pp 1039–1042 in Encyclopedia of Environmetrics (ISBN 0471 899976) Edited by Abdel H. El-Shaarawi and Walter W. Piegorsch . John Wiley & Sons, Ltd, Chichester, 2002. 
Lewis, J. R. (1993). Pairs of Latin squares that produce digram-balanced Greco-Latin designs: A BASIC program. Behaviour Research Methods, Instrument, & Computers, 25(3), 414-415 
Ollis, Matt: [http://www.maths.qmul.ac.uk/postgraduate/anncook/ollis(ac).pdf Terraces and the Oberwolfach Problem] 
Prescott, P. (1999). Construction of sequentially counterbalanced designs formed from two Latin squares. Utilitas Mathematica, 55, 135-52. 
Prescott, P. (1999). Construction of uniform-balanced cross-over designs for any odd number of treatments. Statistics in Medicine, 18, 265-72. 
Williams, E. J. (1949). Experimental designs balanced for the estimation of residual effects of treatments. Australian Journal of Scientific Research, 2, 149-168. 
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