ATLANTA (AP) — Since President Barack Obama first won the White House in 2008, political professionals of all ideologies have accepted as truth the importance of using data to win elections.

But presumptive Republican presidential nominee Donald Trump has expressed doubts about that wisdom, saying he'll use data in a "limited" way in the general election. He argues it's his personality that will carry the day.

Here's a look at data in the context of political campaigns.

WHAT IS IT?

Generally speaking, "data and digital" information is used by campaigns to shape strategy and tactics, including early voting and Election Day voter-turnout efforts. It can tap detailed information about individual voters.

Campaigns use the information and their analysis of it to make decisions. Among them: When and where the candidate should campaign? How should advertising dollars be spent? On which television stations (and even which shows) should ads be placed? Which households should get a piece of direct mail? Which should get extra in-person visits from campaign volunteers?

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WHO'S DOING THE WORK? 

It's a big business. Both the Republican National Committee and the Democratic National Committee have spent millions to develop extensive databases of essentially every American voter.

The conservative activist brothers Charles and David Koch have invested their own money in a similar program. And there is an endless list of political consulting firms that help develop and analyze data for parties and campaigns.

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WHAT'S INCLUDED?

Databases start with public records: voter rolls, including voters' participation history and, in states where the information is available, their party registration and race. Census information and other records help identify potential voters who are not yet registered. Also included: a voter's publicly available social media profile.

A typical database has data about consumer habits, the same kind of information that businesses use in marketing.

Campaigns don't necessarily know what a voter bought last week on Amazon, but they almost certainly know what magazines or newspaper a voter reads and might track what a voter says on Twitter during a presidential primary debate.

Every voter in the database is "scored" — or given a numerical assessment that aims to predict how likely he or she is to support a given candidate, party or cause.

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WHAT HAPPENS NEXT?

That baseline data doesn't do much by itself. The value comes in how the analysis of the information guides campaigns to act.

For example, campaign staff and volunteers will make individual contact with voters already identified as likely or possible supporters. They'll record what voters say about candidates, issues and their intentions at the ballot box.

Voter scores are then updated, and additional outreach is planned based on that new set of information.

The DNC's database contains what individual voters told canvassers in past elections, and the RNC recently updated its database with individual voter opinions — even from Democratic voters — about Obama's nomination of federal appeals court Judge Merrick Garland to serve on the Supreme Court.

Campaigns also have other ways to supplement the data. For example, Ted Cruz's GOP primary campaign developed a mobile phone app that collected detailed data from every user who registered to use it.

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THE BOTTOM LINE

The best information is when a voter commits to vote for a specific candidate or, in the case of early voting, confirms he or she has already voted. This and the other information gathered are used by campaigns to "model" — or predict — election results.

In 2008 and 2012, Obama's campaign ran daily models in the months leading to Election Day, with early voting totals added during the final weeks. In 2008, Obama aides said they were not surprised by his victories in GOP-leaning Indiana and North Carolina.

Similarly, Cruz aides said they were not surprised by his victory in this year's Iowa caucuses, despite late polls finding Trump in the lead.

In both cases, the campaigns said, their data operations predicted those results.

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Follow Bill Barrow on Twitter at: http://twitter.com/BillBarrowAP