Definition of the X_HYBRID specificity score. Typical picture of a probe specificity analysis, as available from the MEDIANTE interface (). Each column represents the number of BLAST hits in the MEDIANTE database (blue), Ensembl database (green), RefSeq database (red) for the BLAST expect-value indicated at bottom. The X_HYBRID score for a probe was calculated as the maximal x_hybrid scores among the three databases. Based on expect-values equal to 10, 1, 10−1, 10−2, 10−3, 10−4, 10−15, 10−20, a ‘rank’ was defined, ranging from 0 for an expect-value equal to 10 to 6 for an expect-value equal to 10−15. For instance, the oligonucleotide depicted in has an extra hit in RefSeq for an expect-value of 10−1, thus defining a rank equal to 2. The number of extra hits between the rank and the lowest expect-value is called delta (Δ). In the example shown in , Δ is equal to 1. Δ is always kept in the interval from 1 to 9, meaning that when there are more than 9 extra hits, Δ is kept to 9. A x_hybrid score is defined for each BLAST database (i.e. MEDIANTE, RefSeq, Ensembl) as a decimal number, where the integer part corresponds to the rank, and the leftovers to Δ. The final X_HYBRID score for a probe is defined as the maximal x_hybrid score obtained against the 3 BLAST databases.