Table 1.

Sequential algorithm for the indirect linkage between VQI registry and Medicare claims data.

Step	Center ID	Date of birth	Sex	Procedure date	Zip code
1	x	x	x	x	x
2	x	x	x	x
3	x	x	x	(+/−) 9
4	x	x		x	x
5	x	x		x
6	x	(+/−) 3	x	x	x
7	State	x	x	x	x

The first step matched with all five variables. The algorithm then accounted for missing and inaccurate variables by allowing some flexibility in dates of birth and procedure and indirect identifiers used.