The decimal logarithm of significance level.

The oligonucleotide motif is considered significant, if it meets the following conditions:

(1) the fraction f of the RGS containing the motif is higher than a certain level fo and

(2) the binomial probability P(n,N) to observe this motif by accidence in n and more
number of RGS from N RGS considered, is lower than a significance level a.

We recommend to use lg(a)>-8.