NEW YORK: Voters who click on President Barack Obama’s campaign website are likely to start seeing display ads promoting his re-election bid on their Facebook pages and other sites they visit. Voters searching Google for information about Mitt Romney may notice a 15-second ad promoting the Republican presidential hopeful the next time they watch a video online.

The 2012 election could be decided by which campaign is best at exploiting voters’ Internet data.

The Romney and Obama campaigns are spending heavily on television ads and other traditional tools to convey their messages. But strategists say the most important breakthrough this year is the campaigns’ use of online data to raise money, share information and persuade supporters to vote. The practice, known as “micro-targeting,” has been a staple of product marketing. Now it’s facing the greatest test of its political impact in the race for the White House.

“The story of this presidential campaign will be how both sides are using data and algorithms and personalisation and math in their marketing,” said Adam Berke, president of the digital retargeting company AdRoll. “The promise and beauty of it is that it’s highly measurable — it’s easy to collect data and see what’s resonating and not resonating with voters.”

Campaigns have worked for years to target subsets of voters using commercially available demographic data, ZIP codes, shopping preferences and television viewing habits. But the growing sophistication of data-mining tools has allowed campaigns to dig deeply into voters’ online habits, giving politicians an unparalleled ability to personalise messages for individual voters.

Officials in both presidential campaigns declined to discuss their digital strategy, but a review of their most recent Federal Election Commission reports shows both campaigns spending heavily on it. The Romney team spent nearly $1 million on digital consulting in April and Obama at least $300,000.

Both campaigns have been building their digital operations, but the Obama team, famous for its use of the Internet to raise money and build its grassroots network in 2008, has a significant edge. Obama’s digital staff is far bigger than it was four years ago, bringing aboard engineers and others with backgrounds in statistics and quantitative analysis to assist with the online development.

Among other things, the Obama team is using micro-targeting to enhance its voter turnout program. The campaign on Wednesday unveiled Dashboard, a new tool for field organisers and volunteers to collect data about voters both online and in person and deliver it back to a centralised campaign database.

Romney’s campaign will likely receive a digital assist from the Republican National Committee and conservative-leaning independent groups that are working to build databases to target like-minded voters.

Television advertising continues to be one of a campaign’s largest budget items, but a TV ad is a blunt instrument hitting a large number of people at one time — many of whom won’t vote or don’t support the candidate who is buying the ads.

Online microtargeting, by comparison, is far less costly and touches only those the campaign wants to reach.

“It’s used to prevent campaigns from wasting time and money on people who won’t vote for them anyway,” said Jeff Coleman, a digital developer and former field organiser for Obama’s 2008 campaign.

Campaigns use microtargeting to identify potential supporters or donors using data gleaned from a range of sources, especially their Internet browsing history. A digital profile of each person is then created, allowing the campaigns to find them online and solicit them for money and support.

Online searches offer campaigns the simplest form of targeted advertising. When a voter searches on a candidate’s name or a keyword that indicates interest in that candidate, campaigns will place ads next to the search.

The ads offer a great return on investment because the campaign only has to pay for the ad if the voter actually clicks on it. By layering additional data about the person who clicked on the ad, such as their gender or geographic location, the campaign can tailor a very specific message to get that person’s attention.

“Campaigns used to look at search advertising only if they could raise money off it or use it as a substitute for direct mail. We’re now seeing campaigns use search ads for persuasion and mobilisation,” said Rob Saliterman, a former aide to President George W. Bush who handles Google’s advertising sales and outreach efforts to Republican campaigns.

The campaigns also use micro-targeting to determine the placement of display ads, the small boxes that appear on websites and follow users around as they browse the Internet.

The campaigns might choose specific sites that are likely to attract voters sympathetic to their candidate. The Romney team might place a display ad on a conservative news website, while Obama might do so on a site popular with college students.

Retargeting, or reaching out to someone who has indicated an interest in a candidate online but has not yet taken an action, is another way campaigns use display ads to reach potential supporters. People who have visited a candidate’s website but left the site without signing up or making a contribution might start seeing display ads from the campaign urging them to do so.

Campaigns will also place display ads on websites targeting a voter’s interests unrelated to politics, such as nature or sports or cooking.

The video-sharing site YouTube has become a popular site for campaign advertising as more people migrate from watching live television to viewing shows and other videos online. Google, which owns YouTube, receives its largest share of political advertising revenue from YouTube ads, Saliterman said.

A voter who has indicated an interest in a candidate and then views a video on YouTube is likely to see a 15- or 30-second campaign ad, called a pre-roll, pop up. A box will appear after 5 seconds asking if the person wants to continue viewing the ad. Campaigns only pay for ads the viewer watches through to completion.