Table 5.

Characterization of the primary source of error for several linkage variables in our data set

Sensitivity	Variable	Primary source of error
86.5%	Social security number	Missing entries
93.1%	First name	Greater use of nicknames in an outpatient setting
94.5%	Social security number when present	2/3 typos, 1/3 invalid (900–999 prefix)
95.2%	Last name	Marriage
96.7%–97.2%	Composite identifier	Spelling variation in initial letters
99.7%	Date of birth	Typos