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Table 1 Definition of Matching Classes from the NDI

From: The general social survey-national death index: an innovative new dataset for the social sciences

Class 1: Exact match on SSN, (all nine digits), first name, middle initial, last names, sex, state of birth, birth month and birth year.

Class 2: Class 2: SSN matches on at least seven digits and one or more of the other items from Class 1 may not match.

Note: Some matched cases are moved from Class 2 to Class 5 because of an indication that the reported SSN belongs to the spouse. This includes those cases for which the SSN is known and matches, but the first name and sex do not agree.

Class 3: SSN unknown but eight or more of first name, middle initial, last name, birth day, birth month, birth year, sex, race, marital status, or state of birth match.

Class 4: Same as Class 3 but less than eight items match.

Class 5: SSN is known but doesn't match.

Note: Some matched cases are moved from Class 5 to Class 3 because of an indication that one of the SSN's (on the user record or on the death certificate) may have been reported incorrectly but a significant number of other data items are in agreement.