(Readers who don’t require the nuts-and-bolts math for every concept of an algorithmic technique can skip this section.)
The type of statistical property that addresses questions of the probability that events or properties happen—given the context of other events’ or properties’ existence—is known as “conditional probability.”
Probabilities of the form “The probability that the word ’foo’ appears in a spam message” are more precisely stated as “The probability that a message is spam given the word ’foo’ in its text” and are written like this in statistical mathematics:
or, more concisely,
A simple pair of tables of word counters ...