The Margin of Error procedure calculates the Margin of Error inherent in the number of completes you have generated thus far. The margin is indicated at four levels of confidence. Generally, comparisons in margin of error are made at the 95% level of confidence, which means there is a 95% chance that the results you are seeing are accurate +/- the margin percentage. (There is a 5% chance that the values you are seeing are entirely outside this range.)

Margin of Error screen

You can change the sample size used in calculating Margin of Error by clicking the up and down arrows in the spin box, or typing in your sample size directly. As the sample size changes, so too will the Margin of Error for each of the four levels of confidence.

The Margin of Error calculator uses a market size base of 2.5 million people to perform its calculations. For a more precise calculation for your specific market, please call ComQuest. It is possible to customize the population base of the universe used in the calculations within the ComQuest program, although it will not alter the Margin of Error by more than a tenth of a point or so in most cases.

Obviously, as the sample size increases, or the Level of Confidence decreases, the Margin of Error will increase.

To cut the margin of error in half, you must quadruple the size of the sample.

For a very good explanation of how Margin of Error affects the results of research and polling, we highly recommend downloading and reading the PDF file available on-line at:

http://www.amstat.org/sections/srms/brochures/margin.pdf