You want the positives to sum to 1 and the negatives sum to 1.

Best Regards, Donald McLaren
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and Harvard Medical School
Office: (773) 406-2464
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On Tue, May 10, 2011 at 4:59 PM, Andrew Westphal <[log in to unmask]> wrote:
Dear Dr. McLaren,

Thanks for responding to me. The design is event-related with varying numbers of sessions due to blocks being removed due to movement and such. Is the weighting with whole integers still a problem in the second level analysis if the contrast sums to zero? For example, 2 session subject (1 -1 0 0 1 -1 0 0) and 5 session subject (1 -1 0 0 1 -1 0 0 1 -1 0 0 1 -1 0 0 1 -1 0 0).