# Margin Ratios in Polling - Question (No Politics)

Discussion in 'Archived Threads 2001-2004' started by James_S, Nov 6, 2001.

1. ### James_S Second Unit

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Can someone please explain the +/- margin in elections, I don’t want this to turn into anything political just curious, and I am no math genius nor do I claim to be.
Example A: If a 1000 people are polled and lets say Candidate A gets 50% and Candidate B gets 44% and there is a +/- ratio of 4.5%. How can that be a dead heat?
Example B: If a 1000 people are polled and candidate receives 500 votes or 50% of the vote and Candidate gets 440 votes or 44% and the there is 60 people (6%) undecided how can there be a margin of error, lets say of 3.5%?
Is it human input or ?????.
Thanks for the help!
James
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Example A:
If the margin of error is 4.5 percent, then they are saying that Candidate A's actual percentage could range from 45.5 to 54.5 percent of the vote.
Candidate B could range from 39.5 to 49.5 percent of the vote.
Candidate A and B's ranges overlap. Therefore, there are points in that range where both candidates could have an equal percentage of the vote.
For example, both candidates could have 48 percent of the vote, leaving 4 percent undecided.
- Steve

3. ### Brian Perry Cinematographer

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In addition to what Steve said, the margin of error depends largely on the sampling size. The more people sampled, the less the margin of error.
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5. ### Denward Supporting Actor

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[propellor beany]
[/propellor beany]
You learn this stuff when you start taking stats in college.
To relate this just slightly to actual recent events, even elections are samplings (since only some people vote) which are subject to margin for error. So even though Gore got more of the popular vote than Bush nationwide and Bush got more of the votes in Florida, neither one of them probably has a valid mathematical argument that the country or Florida liked him better.
[Edited last by Denward on November 07, 2001 at 02:42 PM]

6. ### CharlesD Screenwriter

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As the other replies indicate a poll is an exercise in probability. IF a poll says 45% of people prefer chocolate ice cream to vanilla and has a margin of +/- 5%, it is really saying that there is a 90% chance that somewhere between 40 and 50 % of people prefer chocolate ice cream to vanilla. The 90% "confidence" figure in this example is based, IIRC, on the size of the sample (generally the confidence if 90 or 95%).
The calculation of these figures is based on solid mathematics, people who don't like the outcome of a particular poll (esp. political ones) basically don't understand the mathematics.
If you pay attention the election results next year, you will see that the results of at least 95% of the various House and Senate races will fall within the predicted margin of error.
They key to an accurate poll is having an appropriately sized sample, and that sample must be truly random. Getting a truly random sample is the hardest part, and good polling organizations go to extreme lengths to achieve this.
Another factor in polling is the wording of any questions. Sometimes polls are conducted with the purpose of supporting a particular cause/view and the questions are worded in such a way to yield a desired result. Microsoft once allegedly conducted a poll that showed a large majority of programmers supported their "right to innovate", but to get their desired result they had to concoct a several paragraph "question". Other, more straight-forward wordings, yielded results no-where near what Microsoft wanted.
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7. ### James_S Second Unit

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Got It, I figured somebody would know.
You guys are the Best!!!
Thanks
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Do you spend time with your family.....
Cause a man that doesn't spend time with his family can never be a real man.
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9. ### CharlesD Screenwriter

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Denward,
I meant that at least 95% of the actual results would fall within the range predicted by the polls. I would imagine that the polls are conducted have a 95% confidence factor, and from observing the results of (House and Senate) elections over the past few cycles, I would say that at least 95% of the predictions from the polls turn out to be correct.
This of course includes situations where the Poll predicts candidate A wins, but has a lead of less than the margin of error, but Candidate B wins and the percentage of actual votes cast for each candidadte falls with in the predicted range.
I have never formally counted the numbers of success vs failures, this is just my observation. Certain groups tend to distrust polling, especially when the results don't agree with their particular world view, so I have paid particular attention to just how accurate these polls turn out to be so that i can be confident that they are wrong.
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10. ### Denward Supporting Actor

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Ooops. My bad, Charles. I misunderstood your post. FYI, I found a site with 2000 election results and of the 435 House races, 60 were won with

11. ### Dave Morton Supporting Actor

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Actually, these things follow a binomial distribution where the standard deviation is square root of (np(1-p)) where p=probability or percentage of the candidate of interest. Then we take that value and divide by the square root of n, the sample size. This will give the standard error of the distribution. Thus as someone says, the sample size does make a difference. The larger the sample the smaller the standard error. It is really a measure of the dispersion of the data.
OK, I'm a statistician and I can really geek out with this stuff.
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