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Let's clear up misinformation about Polling Margin of Error

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TruthIsAll Donating Member (1000+ posts) Send PM | Profile | Ignore Wed Nov-17-04 10:02 PM
Original message
Let's clear up misinformation about Polling Margin of Error
Edited on Wed Nov-17-04 10:04 PM by TruthIsAll
Let's clear up misinformation about Polling Margin of Error.

The greater the sample size the more accurate the estimate,
since the MoE decreases as the sample size increases. 

The MoE is equal to 1.96 * the standard deviation (Stdev)
The Stdev is a measure of dispersion around the sample mean.  

A typical national poll samples 1000-1200.

It makes NO difference whether one is sampling a city,  state
or the nation. The ONLY thing that matters is the number of
people sampled, not the SIZE of the underlying population
(city, state, or nation).

Exit Polls taken are more accurate than standard polls.
The exit polls sampled more than 2000 people in the critical
states.
An exit poll of 2000 people has an MoE of LESS than one
percent.

The statistics supplied below are applicable to STANDARD
pre-election polls. 

For any sample size, the sample mean will be within the MoE of
the actual population mean 95% of the time.

For a 1000 sample size, the sample mean will be within 3.10%
of the actual mean 95% of the time.

For a 2000 sample size, the sample mean will be within 2.19%
of the actual mean 95% of the time.

And so on...


Sample	Sample	Std
Size	MoE	Dev

1000 	3.10%	1.58%
1250 	2.77%	1.41%
1500 	2.53%	1.29%
2000 	2.19%	1.12%
3000 	1.79%	0.91%
		
4000 	1.55%	0.79%
5000 	1.39%	0.71%
6000 	1.27%	0.65%
7000 	1.17%	0.60%
8000 	1.10%	0.56%
		
9000 	1.03%	0.53%
10000 	0.98%	0.50%
11000 	0.93%	0.48%
12000 	0.89%	0.46%
13000 	0.86%	0.44%
		
14000 	0.83%	0.42%
15000 	0.80%	0.41%
16000 	0.77%	0.40%
17000 	0.75%	0.38%
18000 	0.73%	0.37%
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TruthIsAll Donating Member (1000+ posts) Send PM | Profile | Ignore Thu Nov-18-04 09:56 AM
Response to Original message
1. am kick
tia
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NewYorkerfromMass Donating Member (1000+ posts) Send PM | Profile | Ignore Thu Nov-18-04 10:10 AM
Response to Original message
2. What about the sampling bias of 59% women?
I stated elsewhere and will say here- even if the exit polls were comprised of 59% women it would make little or no difference, because most married women were shown to have backed Bush, and it is more likely that they would have voted earlier in the day to be back at home with hubby and kids in the evening.
SO I say that excuse is BS.
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msongs Donating Member (1000+ posts) Send PM | Profile | Ignore Thu Nov-18-04 10:22 AM
Response to Original message
3. nice data but the DNC does not give a damn about any of this, they
have bent over and spread their legs again......after all, every sadist like Bush needs a willing masochist like the DNC.

Msongs
Riverside Ca

See our political t shirts!
www.msongs.com/political-shirts.htm
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Captain Ron Donating Member (11 posts) Send PM | Profile | Ignore Thu Nov-18-04 10:33 AM
Response to Original message
4. Just for grins (and to be a PITA) ...
... let's just say the DNC/Kerry campaign found out exactly where and exactly when exit pollsters would be interviewing. Let's also say that they flooded those locations, at those times, with pro-Kerry supporters.

What would that mean wrt sample size, MoE, Stdev, poll accuracy, etc.?
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NewYorkerfromMass Donating Member (1000+ posts) Send PM | Profile | Ignore Thu Nov-18-04 10:37 AM
Response to Reply #4
6. There would be no logical reason whatsoever to do that
WTF?
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Captain Ron Donating Member (11 posts) Send PM | Profile | Ignore Thu Nov-18-04 10:58 AM
Response to Reply #6
8. I'm not saying it happened, but
the plan could have had two desired effects:

1) If Kerry lost, it certainly could create the perception of fraud. Just look at this thread, as well as many others.

2) Leaked exit polls (which hid happen) could have supressed subsequent votes feeling the result was already concluded.

Don't get me wrong, I'm 100% behind the charges of fraud and the desire to find the truth and do not want anybody to lose interest. I just wish the media would pursue the issue as strongly as members here are. I might even be willing to contribute to TV commercials that make sure everyone knows about these charges. I would even support some of the more involved members of DU be chosen to plead the case.
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newyawker99 Donating Member (1000+ posts) Send PM | Profile | Ignore Thu Nov-18-04 11:25 AM
Response to Reply #8
10. Hi Captain Ron!!
Welcome to DU!! :toast:
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nancyharris Donating Member (637 posts) Send PM | Profile | Ignore Thu Nov-18-04 10:33 AM
Response to Original message
5. Logically
The ONLY thing that matters is the number of people sampled, not the SIZE of the underlying population

This makes no sense. With exit polls, what matters is WHERE the polls are taken. Exit polls are not universal. They are targeted at key precincts that the pollsters believe will provide an accurate sample for the whole state. If the demographics in those particular precincts has changed since the last election (or if the pollsters choice of targeted precincts is not accurate) that inaccuracy will be reflected in the polling.

Just how many precincts were exit polled in NH, OH, FL CO and WV? And which precincts were polled? MOST IMPORTANTLY, how closely does the exit polling for a particular precinct reflect the actual vote for that precinct? The answer to these questions will reveal the true story behind the exit polling discrepancies.
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KittyWampus Donating Member (1000+ posts) Send PM | Profile | Ignore Thu Nov-18-04 10:47 AM
Response to Reply #5
7. Well, Since Exit Polls Were Correct Up Til Bush, We Should Also See
to what extent methodology did OR DID NOT differ from years past.

Remember, the Exit Polls in 2000 were correct, Gore won with more votes in Florida... but they stopped counting legal ballots until after SCOTUS appointed Bush.
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pmbryant Donating Member (1000+ posts) Send PM | Profile | Ignore Thu Nov-18-04 11:24 AM
Response to Original message
9. Statistical margin of error isn't the only problem
Sampling biases can be just as big or even bigger than the statistical margin of error.

For an extreme example, polling 1000 people at a Bush rally does not result in a true margin of error of only a few percent, as the statistical error would indicate.

--Peter
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