What is it?

Interstate Voter Registration Crosscheck (commonly referred to as IVRC or Crosscheck) is database software designed to compare voter records from member states and identify voters registered in two or more states.

Crosscheck was developed by the State of Kansas in 2005 by then-Secretary-of-State Ron Thornburgh in concert with three neighboring states to compare voter registration data and identify any Americans who may have voted twice in recent elections.

Current Kansas SOS Kris Kobach oversaw the expansion of Crosscheck to a peak of 29 states in 2014.  In 2017, 28 states submitted a combined 98 million voter records for analysis.


The process

Every year, member states upload voter registration data to Kansas including voter name, date-of-birth (DOB) and last four digits of social security number (SSN4).

Kansas combines all member states' data into one large database, searches for duplicates, and produces for each state a report of all "Potential Duplicant Registrants".

States download their reports, then delete their data from the site hosted by Kansas.  


Validly registered American voters are placed on the Crosscheck report if they match another voter in a Crosscheck state on just three things:  first name, last name, and full date-of-birth.

Even if the last four digits of the social security number (SSN4) don't match, two voters who share a first name, last name and date-of-birth (DOB) are considered a "Potential Duplicate Registrant".  

Similary, if two records share a first, last name and DOB but mismatch on middle name and suffix (Jr/Sr), they are also considered a "Potential Duplicate Registrant". 

An example makes this more clear: 

  • Susan Smith of Kansas born 5/6/1956 (SSN4 = 7654) and
  • Susan Smith of South Dakota born 5/6/1956 (SSN4=3435)

are reported to both Kansas and South Dakota as "Potential Duplicate Registrants".  Each false positive is two voters put at risk.

The Fatal Flaw: social security number is ignored


the result: Voters at risk

A 2011 White Paper published by ID Analytics concluded that attempting to identify unique individuals using only first name, last name, and DOB "fails for practically all common American names".  

Consistent with that finding, analysis of Crosscheck data released in various public information requests and other public reporting suggests that between 60-90% of voters listed as "Potential Duplicate Registrants" have mismatched or missing SSN4 or middle names.  For details and analysis, please see Virginia and Iowa


Crosscheck in 2017 referred 7,214,664 pairs of "Potential Duplicate Registrants" back to member states.  Each pair is presented as being a single voter who is registered in two states.

If the match is correct, that is true.  

If the match is in error, each "pair" represents two distinct voters who are validly registered in their home state.  

Data from Virginia and Iowa suggests that at most 40% of  Crosscheck data (2,885,866 pairs in 2017) is correctly matched and could reasonably be considered worth looking into whether it is a doubly registered voter.

And that is the best case scenario!

How many at risk?