5-1.1 Presence dependence.
Besides reliability and coincidence there are at least two
additional factors that influence the outcome probability of a given comparison weight. One factor
is the presence of data in a field (pi). We need to account for the fact that the presence of data in one
particular field may well depend on (or affect) whether there is data present in some other field.
Expecting to have a value in one field of a record may not make sense whenever there is no value
in some other field. We say then that the first field is dependent on the presence of data in the
second; there is presence dependence between the two fields. For example, the day of the month
is seldom present unless the month is also present, and the month of the year is seldom present
without the year also being given.
