[Egon]

Flip-Ping.

[Ole Okie]

Glad to see you post this, IowaHawk.

[RabbitMan]

Thank you for this info. Quick question: does the margin of error mean that I go either side of the stated value, or is it the total range of error? For example, if a candidate polls at 50% with a 3% margin of error, does that mean that 95% of the time the actual value will be between 47% and 53%, or between 48.5% and 51.5%?

[2ndreconmarine]

Since this is a nice probability primer, I would like to add some other statistical issues with sampled polls: The big problem with the MSM journalists is that they have never had a math course and do not understand sampled probability systems. For example, they talk about MOE as if it were binary: inside is statistical dead heat, outside is an incontrovertable fact. The reality is, of course, that the polls are samples of a population and are only approximate. Practically: if you sample the same population many times, you will get different answers and those answers will vary according to a distribution. Therefore, you should expect sample variations.

1. The MSM problem is that they see a change and assume it is real. They are responding to their own statistics.

2. Usually, they quote one poll. By contrast, the many, excellent analyses done here on FR usually consider the average of multiple polls.

3. The excellent FR analyses I have seen here consider poll biases as well as the precisions. Most polls assume a zero-bias.

4. The bias effects can be mitigated by considering trend lines over some period and multiple polls.

[codercpc]

When we see the majority of polls within the MOE yet still with Bush leading, does that mean anything statistically.

Lets say 5 polls with a MOE of 3% have B 49 K 46, and 2 polls with K 49 B 46, does President Bushs chances of winning increase statistically? I hope you understand the question, I don't exactly know how to put it in words, but do "averages" like RCP mean anything?

[bjc]

I could not agree more. What is truly amazing is the self-delusion of the pollsters and thier willingness to be knowingly deceitful - reminds me of Kerry!
Lets vote and get it over with.

[sauropod]

read later with coffee

[lunarville]

Please note that the "length of Zogby's goat entrails in furlongs" is accepted datum in French mathematics as represented by the symbol (Zg~~...)

[Enlightiator]

This is probably the best post I have ever seen stating why the "margin of error" in the polls is baloney - the poll accuracy (margin of error) assume random samples that ACCURATELY reflect the populace, and you give some of the reasons they do not. The proof of this is quite evident when you notice that sometimes different polls taken at the same time span vary by a huge margin, outside of the MOE.

Another source of error is introduced when the pollsters "adjust" and "weight" the responses for demographic, sex, and other factors.

Even a margin of error of +/-4% if it were truly accurate MOE with a 95% confidence interval, means that a 52B to 48K vote might actually be a 52K to 48B vote! But with the numerous other errors as described in your post, I would put the REAL MOE more like +/- 8%. Ronald Reagans landslide win his second time around showed just how bad polls can be, he beat some of them by 10%!

The accuracy of the polls increases with sample size, and the best bet is to trend the poll and look at the trends of numerous polls. When you do that, Bush wins :)

[Ilya Mourometz]

I followed most of this, but what is the "sqrt" value?