For example, using Eq. (3), protein identification with a probability of 10−10, that it is a misidentification will have a MOWSE score of 100. The probability is calculated based on the number of peptide matches identified for a particular protein match, compared to the sequence database using an algorithm detailed by Pappin et al. (1993). To determine whether a particular MOWSE score is significant, a cut-off value is defined based on the assumption that a random event is acceptable if it occurs less than 5% of the time. To calculate the cut-off MOWSE score, the probability of a random event needs to be calculated across the whole of the protein database that is searched for matches. At the time the LC–MS/MS results were submitted the NCBI protein reference database contained 11,961,441 sequences. A 5% probability of a random identification is equivalent to 1 in 20 mismatches, so the MOWSE cut-off score will be