Moment, Linger On

Understanding political polls, part one: 1 out of 20

With all the interest in this year's election there are a good number of people who are driven into a frenzy with all of these polls, trumpeting the latest poll results and assigning a good deal of meaning to them. There are other, more cynical, people who refuse to believe that anything meaningful could be gained from polling such a small number of people, especially when they are never called themselves. Over the next few days I'll try to explain how these polls work with an eye to answering the following questions:

1. What does the margin of error mean?

2. How is it calculated?

3. Are polls always correct?

4. How many people are really needed to accuately poll?

5. Why do polls by different organizations always seem to differ in similar ways?

Today I'll try to briefly answer questions one and three.

What does the margin of error mean?

The margin of error (or MOE) in the poll is the range that you can expect reality to differ from the results of the poll. For instance, if a poll between Bush and Kerry results in Kerry 48% and Bush 44% with a MOE of 3% then the real split in the entire population should be somewhere between 45% and 51% for Kerry and somewhere between 41% and 47% for Bush.

Are polls always correct?

No. There is a magic number built into every poll called the confidence interval. For political polls the confidence interval is 95%, which means that the poll will be within the margin of error 95% of the time. (For medical or engineering tests, where the results matter, the CI will often be 99% or higher. For politics 95% is good enough.) What this means, and nobody ever mentions this, is that one out of evey 20 polls should be way off base with reality differing from the poll by more than the margin of error.

Next: How is the margin of error computed?

A challenge for Bush supporters

I'm not persuadable at this point. I'm going to be voting for Kerry no matter what. But pretend for a second that I was. Think of this as a chance to fine tune your arguments before going after someone who is still undecided.

My challenge, then, is this. Come up with just one example from George Bush's life that could cause me to believe that he is a decent human being. Just one. And abstract nonsense like "I admire his faith" or "I think he would never lie to me" or "I think he is a good parent" or "I like his stance on position X" doesn't count. I'm talking about one specific thing that he has done in his life that would make me think that he is a good man.

I'll give you an example for John Kerry. I admire John Kerry because he volunteered to serve in combat in Vietnam when he could have easily avoided doing so. Now you can come back at me with all sorts of stuff about whether he deserved his silver star or not or how you don't like how he came out against the war after he came back or whatever. But his going in the first place, I would maintain, was an objectively good thing to do and a credit to his character.

Come up with just one example for Bush for me. Just one. And until you do I will continue to believe that, like Carville said, Kerry is just a better man than George Bush.