Subset Ratio is the number of unique occurrences in the table in question as compared to the total number of unique occurrences in all tables. See the example below there are five unique occurrences in the field F1 (numbers 1-5). The subset ratio in table A is 60% (3/5, ie 3 unique occurrences as compared to 4 rows in the table). In table B the subset ratio will be 80% (numbers 1, 2, 4 and 5 as compared to the total the numbers 1-5, ie 4/5).

 

A:
LOAD * INLINE [
F1, F2
1, A
2, B
3, C
3, Cbis
];

B:
LOAD * INLINE [
F1, F3
1, I
2, II
4,  IV
5, V
];