Campaign 2016: Why polling results can differ

CINCINNATI (WKRC) - The candidate trailing in most national polls is complaining that some of those polls are stacked against him.

Donald Trump is adding "voter surveys" to his list of unsubstantiated claims the election is rigged.

As early voters showed up at the Hamilton County Board of Elections, polling organizations were trying to figure out how the citizens and others on Election Day will cast their ballots. The website Real Clear Politics averages major national polls and shows Hillary Clinton up by around six percent. With individual polls ranging from Trump up two to Clinton up twelve.

Political experts say the overall direction in recent weeks is more significant than one poll versus another.

Professor Mack Mariani of Xavier University said, “I think that the trend lines are more important than any particular poll, and in this case the trend lines show Hillary Clinton is gaining and Donald Trump is, if not fading, not moving forward.”

But Trump, who bragged about positive polls during the Republican primary, is now criticizing those which show him losing. Polls are indeed weighted, not to prejudice the outcome but based on the pollster's best estimate on what the electorate will be.

“You don't want to see too many elderly people, but they're the ones who are most likely to be home and have a land line, most likely to be picking up the phone. Young people are harder to get and so pollsters will make certain assumptions about what the electorate is going to look like on Election Day,” said Mariani.

Two important things to remember: polls in key battleground states like Ohio, North Carolina, and Florida are more important than the national polling numbers. Ohio is basically a tie right now. Also, remember each poll has a "margin of error." For example, if the margin of error is plus or minus four percent, which means a 50- 50 tie could really be 54- 46 or anything in between.

One more complicating factor for the polls, the two other presidential candidates Libertarian Gary Johnson and Green Party candidate Jill Stein. Both could impact the Clinton-Trump race in states that are close.