If two events are unrelated so that the occurrence (or non-occurrence) of one of the events doesn't affect the likelihood of the other event, the events are called
independent. We say that two events are independent if and only if (iff)
P(Pi and M) = P(Pi) × P(M)
To see why this reflects our intuition about independence, combine this with the rules for AND, i.e.,
being matched (M) has no effect on whether data is present in the field (Pi), or symmetrically, Pi has
no effect on M.
iff P(M) = P(M | Pi) or iff P(Pi) = P(Pi | M)
This means that when the data values in the fields of a record are independent, their combined
probability is the product of their individual probabilities.
P(A1 and A2 and A3 and . . . ) = P(A1) × P( A2) × P( A3) × . . .
