The percentage of Oahu voters casting ballots in the biennial Neighborhood Board elections increased slightly this year, the third such election conducted entirely online and by phone.

In the election last month, 15,318 residents voted. That was 8.61 percent of registered voters, up from 8.47 percent in 2011 (when 13,264 people voted) and 6.5 percent in 2009.

However, those percentages represent a sharp decrease after a switch to a paperless system in 2009.

Twenty-eight percent of eligible voters voted in the 2007 election. The "distinct drop-off" shows a resistance in elderly residents toward online voting and a "general apathy" among registered voters, said Nicole Velasco, executive secretary of the Neighborhood Commission.

The issue has prompted many letters to the Neighborhood Commission, Velasco said, including privacy fears about entering the last four digits of Social Security numbers via Internet and phone keypads.

In 2007 the commission offered voters the option of voting with a paper ballot or online, she said. The change was due to costs, such as the price of postage.

The commission has saved more than $100,000 each election year.

Oahu’s 33 neighborhood boards gauge community sentiment on development, transportation and other issues. They are administered by the Neighborhood Commission, a city agency.

Of the 439 seats up for election this year, 388 were filled in last month’s election. The remaining 51 seats, vacant because there were no candidates, will be filled by appointment by the boards after the new term begins July 1, a news release said.

This was the third neighborhood board election using an online voting system by Everyone Counts Inc.

Election results and board vacancies can be found at www1.honolulu.gov/nco; click on "Election Results" near the top of the page.