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Just say no!

We can express a consensus sequence in bits and so quantify the effect of making one. Each unique base (A, C, G or T) of a consensus counts as 2 bits. When two variations such as C or G are allowed (e.g. Fig. 3) we count 1 bit; there is, of course, no small-sample correction. 3 bases would count as [Schneider et al., 1986], and 4 bases (N) would be zero. Plotting the total information of each sequence logo shown in this paper against this `consensus information' we obtain Fig. 7 (summarized in Table 1 ). The figure shows that the consensus is always larger than the information content, even drastically so. However, the consensus could be tweaked (in individual cases) by arbitrarily playing around with the rules [Day & McMorris, 1992] to reduce the number of bits. But all the tweaking in the world will never give the proper weights because the frequencies are always rounded to obtain a consensus sequence. The examples in this paper show that when faced with the prospect of using a consensus sequence, we should `just say no'.