The presence of the various fields in a date is clearly dependent. As an example consider the death date field in a database of records from Akershus, Norway. The day (d) appears 9.03% of the time, the month (m) appears 9.32% of the time, and the year (y) appears 10.9% of the time. The probability of data being present in two records being compared is the square of this value. Since it is outcome probabilities for comparisons that we are interested in, we make these values the respective p values.