Bogofilter's Spamicity Calculation Methods Bogofilter offers three methods of computing a message's "spamicity," a number, ranging from 0 to 1, that gets closer to 1 as the likelihood increases that the message is spam. We call these: the Graham method the Robinson method the Robinson-Fisher method The Graham method computes the probability that each word in the message indicates spam or non-spam, then selects the words with highest probabilities and computes the spamicity. This gives a range of spamicities from 0.01 to 0.99, with values over 0.9 indicating spam. The Robinson method computes word probabilities in much the same way as the Graham method, but deals more cleanly with cases where a word has been encountered few, or no, times in the past. This method gives a range of spamicities between 0 and 1 (not inclusive), but the numbers tend more toward the center of the range. Consequently, spamicities over approximately 0.54 indicate spam. The Fisher method is a variant of the Robinson method that uses a statistical chi-square calculation as the last step. This method tends to yield results very near 0 for non-spam and very near 1 for spam. Messages that aren't clearly identifiable produce results in the range of roughly 0.1 to 0.95. This method is called Robinson-Fisher because the calculation is based on Fisher's method, published in the 1950s, for combining independently derived probabilities. When building bogofilter, the user can specify (at configuration) any or all of the above methods for inclusion in the program being built. The method to use when running bogofilter can be specified on the command line or in the configuration file.