(CNN) -- With a week and a half to go until Election Day, a new poll indicates the race for arguably the most important battleground state remains very close.

According to a CNN/ORC International survey released Friday, President Barack Obama holds a four point advantage over Republican nominee Mitt Romney in the contest for Ohio's much fought over 18 electoral votes.

Fifty-percent of likely voters questioned in the poll say they are backing the president, with 46 percent supporting the former Massachusetts governor. Obama's four point advantage is within the survey's sampling error. The survey was conducted Tuesday through Thursday, entirely after Monday's final presidential debate.

"The race in the Buckeye State is essentially unchanged since early October, when a CNN/ORC poll taken just after the first presidential debate also showed President Obama with a four-point margin over Governor Romney," says CNN Polling Director Keating Holland.


Surveys by other organizations conducted last month, before the first debate, had Obama ahead of Romney by seven to 10 points.

The new poll indicates that Obama has a double digit lead among those who have already voted absentee or early ballot or plan to do so before Election Day, with Romney holding the edge among people who plan to cast their ballot on November 6.

According to the survey, the gender gap has tightened a bit, but the basic storyline remains the same. Obama holds a 56-42 percent advantage among female voters, with the GOP challenger up 50-44 percent among men.

"In other major demographic groups, the movement since early October has been in the expected direction, with Obama picking up ground among younger voters, lower-income voters and urban voters and losing support among older voters, suburbanites, and higher-income voters," adds Holland. "Looking at age, for example, Obama has gained three points among voters under 50 years old since early October, but lost three points among voters who are 50 and older."

The poll indicates Obama maintains a small but critical advantage among independent voters. In early October, he had a 50%-46% margin among independents -- virtually identical to the 49%-44% edge he has today

Among those who have voted early or plan to vote before Election Day, Obama holds a 59%-38% lead, with Romney up 51%-44% among those who say they'll vote on Election Day. Ninety-two percent of likely voters say they've made up their minds, with 4% saying they could change their minds.

Campaigning Thursday in Cleveland, the president urged Ohioans to vote early: "Ohio you can vote now, you don't have to vote later."



Ohio was the state that put President George W. Bush over the top in his 2004 re-election. Four years later Obama carried the state by five points over Sen. John McCain. But the Republicans performed well in the Buckeye State in the 2010 midterm elections, winning back the governor's office and five House seats from the Democrats.



This cycle Ohio is seeing an outsized amount of campaign traffic from the presidential candidates. This week alone, Obama campaigned in the state on Tuesday and Thursday. Romney spent Thursday making a swing throughout the state, and returns to Ohio Friday evening.



"Ohio is going to set the course for the nation," Romney said Thursday in Defiance, Ohio.



Overall, the campaigns, party committees, and super PACs and other independent groups have spent more than $118 million to run ads on broadcast TV in Ohio since the start of the general election, with the numbers evenly divided between the two sides. Those figures come from Campaign Media Analysis Group, which tracks political advertising for its clients.



Libertarian Party candidate Gary Johnson, Green Party candidate Jill Stein, and Constitution Party candidate Virgil Goode are also on the presidential ballot in Ohio. When their names were added to the poll, Obama is at 48 percent Romney 44 percent , with Johnson at 4percent, Stein at 2 percent and Goode registering less than one-half of one percent.



The CNN poll was conducted by ORC International from October 23-25, with 1,009 Ohio adults, including 896 registered voters and 741 likely voters, questioned by telephone. The survey's overall sampling error is plus or minus 3.5 percentage points.



American Research Group also released a live operator, non-partisan poll of likely voters in Ohio on Friday. It was also conducted entirely after the final debate. It indicates Obama with a 49-47 percent edge over Romney, which is within the survey's sampling error.