I don't know whether this will work, but it is possible to specify the covariance structure as being based on the correlations, using type=unr.  From there, it seems possible that you could constrain a correlation to be a fixed value. Steve Denham ... View more

You are on the right track with your approach. And in your context, the repeated statement is specifying within-subject variation. But even if you don't use a repeated statement, there is still within-subject variation (a residual variance component). ... View more