Rick Brand Portrait of Newsday reporter Rick Brand taken on

Rick Brand is a longtime Newsday reporter who writes about politics and government on Long Island.

Starting Thursday, combatants in the too-close-to-call 1st Congressional District primary will mass at the final battleground — a warehouse at the Suffolk Board of Elections in Yaphank. The only weapons will be letter openers to unseal nearly 1,800 absentee ballots that have yet to be counted.

Unofficial returns on election night had former Southampton Supervisor Anna Throne-Holst 29 votes ahead of former Suffolk Planning Commission chairman David Calone, a venture capitalist, 5,446 to 5,417. The board of elections sent out 4,110 absentee ballots, of which 1,791 had been returned as of late last week. Votes that arrive by Tuesday will still be counted, if postmarked by primary day.

“The rule of thumb is that if the margin is less than the square root of the number of uncounted absentees, reversing the result is statistically possible,” said Barry McCoy, a Stony Brook University physics professor, a state committeeman and a veteran grassroots operative backing Calone. He said the square root for the absentees is 42, far above Throne-Holst’s 29-vote election night edge.

Calone backers also point out that the majority of absentees comes from two towns that Calone won — Brookhaven, which has 947 uncounted absentees, and East Hampton, which has 206. “That gives us some cause for optimism,” said Jerry Goldfeder, Calone’s elections lawyer.

Throne-Holst’s hometown of Southampton had the second-largest number of absentees with 229, which along with the other five towns she won, total 638 absentees.

Tom Garry, Throne-Holst’s lawyer, said he does not expect widespread clashes. “I seriously doubt either side is going to present significant challenges because that’s not what our party stands for,” he said. “At the end of the day all legitimate votes will be counted. Anna is well known and has represented a good part of the district, so I’m quite confident she’ll win.”

The last time the 1st District had a similar battle was in the 2010 general election between former Rep. Tim Bishop (D-Southampton) and Republican Randy Altschuler. Bishop led by 3,461 votes on election night, later fell behind by 383 and after 36 days was declared the winner by 263 votes after 11,000 absentees were counted. In that effort, Democratic consultants did data mining, such as voters’ charitable contributions and magazine subscriptions, to divine whether voters leaned toward Bishop in deciding which votes to challenge.

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But Garry, who also worked for Bishop, said such efforts are less viable in party primaries because all the voters are Democrats and allegiances are harder to discern, compared to the general election, where data can often identify Republican and unaligned voters who may be leaning Democratic on key issues.

But Rich Schaffer, Suffolk Democratic chairman, said both sides are still calling absentee voters to ask how they voted and to do research on their eligibility. Experts say issues that could emerge include residency of student voters, adult children and those who have summer homes here but also might live and vote in New York City.

However, Schaffer, who is neutral in the race, cautioned against projecting townwide results in assessing absentees. “It’s a real crapshoot,” the party leader said. “Conventional wisdom is out the window because Anna and David both showed unexpected strength where they were not expected to perform.”