Political parties, academics and others purchased over 100 marked copies of the electoral register - which reveals the names of people who did not vote - in the wake of the last general election.
The disclosure came after the Fianna Fáil Minister of State, Mr Frank Fahey, claimed incorrectly yesterday that politicians were entitled to see copies of the register under the Freedom of Information Act.
The used voter registers from all constituencies are sent to the Houses of the Oireachtas after each Dáil election.
The names of non-voters are clearly visible, though the names of those who did vote have a line drawn through them.
However, no information is ever released which in any way reveals how people actually voted, Houses of the Oireachtas sources said. "All of that is confidential, and stays that way," said one.
Information about voting patterns in last year's Nice Treaty referendum is not made available, the franchise officer of the Department of the Environment, Mr Peter Greene, said yesterday.
Unlike the Electoral Act, which covers Dáil, local and European elections, the Referendum Act makes "no provision" for such releases of information, said Mr Greene, who said that he had turned down 12 requests for the marked list in the aftermath of the first Nice referendum.
Fianna Fáil bought a copy of the 1997 general election register as it stood after the close of polling and used it in the last election to draw up maps for party workers and head office to illustrate clearly pockets where the vote was low.
In the wake of the general election in May, parties and academics paid up to €6,000 for the registers of the 42 constituencies, while the records of individual constituencies were also requested.
The charge per constituency depends on the number of seats. The register for three-seaters cost approximately €100, while four-seaters and five-seaters cost €140 and €180 respectively.
"Under the Constitution, the ballot is secret. But the law does not provide the same protection for the register, even though some would argue that a person's decision to vote, or not to vote, should be equally secret," said one source.
From the 1920s to the 1990s, political parties kept track of voting patterns in Dáil elections from information collected by their personation agents, who are entitled by law to be present in polling stations.
On polling day, personation agents are supplied with copies of the voters' register, though they are not allowed to leave polling stations with them so that they cannot improperly use the information.
However, the system became more accurate in the wake of changes made to the Electoral Act in the early 1990s, which allow parties and others to see the register as it stands at the close of polling.
The extra information began to be first used by political parties after the 1997 general election.
Under law, copies of the election register as it stands before polling day are commonly bought by industry, particularly by those compiling direct marketing lists.
Following changes to the Electoral Act last year, voters are entitled to be excluded from lists given to direct marketing companies when they register, or when they change registration details.
