Dear Listmembers, I´m working with metric multidimensional scaling and trying to implement the Torgerson algorithm in SAS/IML. The terms I use are all shown in "Theory and methods of scaling", Torgerson (1958), p.263-268. Torgerson´s P-matrices are first transformed into x-matrices (based on Thurstone´s law of comparative judgment) which contain both estimated differences between stimuli and missing values. Computing the matrix of comparative distances in the next step I meet a problem: In the formula to solve for the comparative distances a few averages summed over different indices are required. Maybe the problem sounds trivial, but I don´t know if the missing values have to be regarded computing the means, or do I simply have to calculate these averages neglecting all missing values. Thanks a lot for your help, Simon Gollick __________________________________________________________________ Gesendet von Yahoo! Mail - http://mail.yahoo.de Logos und Klingeltöne fürs Handy bei http://sms.yahoo.de