Polls don’t “predict” anything

April 12th, 2008 at 01:52pm Pat Cunningham

 

A progressive blog I regularly visit had an item the other day about how a couple of new polls “continue the trend of predicting a narrow Clinton victory in Pennsylvania.”

The polls at issue did no such thing.  No poll ever “predicts” anything.  A poll, if done correctly, is a snapshot of public opinion at a given point in time. 

Even a poll conducted just a few days before an election doesn’t predict anything.  It can be a strong indicator of which candidate is likely to win, but it can’t measure the impact of voters who make their final decisions in the last hours or minutes before the election. Consider the late shift toward Hillary Clinton in the New Hampshire primary, which none of the major pollsters caught.

In the case of the upcoming Pennsylvania primary, the election is still 10 days away.  The polls that my blogger friend saw as predictions probably were conducted several days ago.  Lots can happen between now and election day.

The news media frequently misread poll results. Reporters and editors generally are ignorant of the most basic scientific principles of public-opinion polling.  The public knows even less of such matters.

Take, for example, the margin of error in a given poll. About six months ago, Talking Points Memo, one of my favorite blogs, had this to report: “New ABC News/Washington Post poll shows Obama with lead in Iowa.”

But the poll did not actually show Barack Obama with a lead. It put Obama at 30 percent and Hillary Clinton at 26 percent. That gap of 4 percentage points was within the poll’s margin of error. Hence, the poll showed a statistical dead heat.

As for polls that are conducted online or by any other means in which participants are self-selected — or polls that admit they are “unscientific,” as if that disclaimer justifies their publication as “entertainment” — the results are utterly worthless. 

I’ll never understand why news media that otherwise brag about their dedication to accuracy permit themselves to pass along results of unscientific polls.  Gannett used to do that with an “Annual Teen Survey” in its “USA Weekend” magazine.  (I haven’t seen that mag in years, so I don’t know if it’s still publishing phony polls.)

Entry Filed under: polls