[billswift]

One thing that has always bugged me is how can two polls give different results to effectively identical questions and both claim to have "plus or minus 3%" (or whatever) margin of error, when their results have substantially larger differences than that?

[JacobAldridge]

Keep in mind that defining a representative sample is also fraught with differences. How you you determine if someone is a likely voter (are they registered? did they vote last time? other or some combination of the above?), for example, or ensure what you believe is a representative sample of different ethnicities?

Because a sample of 200 - 1200 is used and multiplied out to represent the population as a whole, tweaks in those definitions can lead to different results for the same questions.

I definitely second the www.fivethirtyeight.com tips, as well as www.electoral-vote.com for regular outside analysis of polls and discussion of methodological differences among the various polling places.

[billswift]

I understand that - I meant my comment to be more a complaint about bogus/worthless "margins of error".

[eru]

The margin of error is often meant as one standard deviation. And for normal distributed data, only around 66% of values lie within that.

[ryanpetrich]

A slight change in wording can change how people think about their answer