Fitting of several commonly used probability distributions to the histogram of LocARNAscan scores. Scores correspond to LocARNAscan alignments using the profile of the RFAM family RF00504 (glycine riboswitch) as input query. The first row shows the fitting of log-normal, gumbel, and generalized extreme value (gev) distributions (red curves) to the alignment scores shown as histogram. The shown scores have been shifted to positive values. In the lower panel, we compare the distributions by Q-Q plots. These plots, which plot the quantiles of the observed scores vs. expected quantiles from the theoretical distributions, visualize in how far two distributions differ in location, scale and skew from each other. All tested known probability distributions (including normal and gamma distribution; data not shown) do not represent the LocARNAscan alignment score distribution well; visible in the Q-Q-plot, since none of the Q-Q plots follows a straight line.