5-2.4 Field presence dependence between two records.

Comparing two records involves a judgement about agreement or disagreement only when the particular field is present in both records. This means that of all the field combinations possible, some will admit comparison even when they are not identical and others will not. Table 2 lists the various specific comparisons for the death date example. A number marks the field comparisons that are equivalent so far as data that may be compared is the same. We need to account for these as outcomes, but missing data disallows comparison. Adding equivalent individual combinations together results in a simple calculation for comparisons.

Death date
Comparison
First Record		 Death date
Comparison
Second Record		 Calculation of
Occurrence of Each
Combination		 Presence
Assuming
Alone		 Calculation of
Occurrence In Pairwise
Comparison		 Presence of
Comparison
Assuming Pairs
[   ] [   ] 1 ( 1 – y ) × ( 1 – y ) 0.7939 (1)   1 – y2 0.9881
[   ] [ Y ] 1 ( 1 – y ) × ( y – m ) 0.0141
[   ] [ M, Y ] 1 ( 1 – y ) × ( m – d ) 0.0026
[   ] [ D, M, Y ] 1 ( 1 – y ) × d 0.0805
[ Y ] [   ] 1 ( y – m ) × ( 1 – y ) 0.0141
[ Y ] [ Y ] 2 ( y – m ) × ( y – m) 0.0003 (2)   y2 – m2 0.0032
[ Y ] [ M, Y ] 2 ( y – m ) × ( m – d ) 0.0001
[ Y ] [ D, M, Y ] 2 ( y – m ) × d 0.0014
[ M, Y ] [   ] 1 ( m – d ) × ( 1 – y ) 0.0026
[ M, Y ] [ Y ] 2 ( m – d ) × ( y – m ) 0.0001
[ M, Y ] [ M, Y ] 3 ( m – d ) × ( m – d ) 0.0000 (3)   m2 – d2 0.0005
[ M, Y ] [ D, M, Y ] 3 ( m – d ) × d 0.0003
[ D, M, Y ] [   ] 1 d × ( 1 – y ) 0.0805
[ D, M, Y ] [ Y ] 2 d × ( y – m ) 0.0014
[ D, M, Y ] [ M, Y ] 3 d × ( m – d ) 0.0003
[ D, M, Y ] [ D, M, Y ] 4 d × d 0.0081 (4)   d2 0.0081

Table 2 — Presence in Death Date Comparisons

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