After publication the author became aware that in an article by J.S. Nicolis, G. Meyer-Kress, and G. Haubs [Non-uniform chaotic dynamics with Implication to information processing, Z. Naturforsch. 38a: 1157-1169 (1983)] the variance of information loss was introduced and was called the "nonuniformity factor." Numerical results for this quantity can also be found there.