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Statistical Tool for Calculating the Margin of Error in Survey Data Analysis

The term "margin of error" can be used to mean
sampling error in general. In media reports of poll results, the term usually refers to the maximum margin of errorfor any percentage reported from that poll. The margin of error is a statistic expressing the amount of random sampling error in a survey's results. The smaller the margin of error, the more trust you can place that the survey's reported results are "true" (that is, representative of the larger population).

Click on your button choice below to launch the appropriate calculator.(Click on the button again to close the calculator)

Margin of Error Calculator - MeansMargin of Error Calculator - Proportions  

There are four important items you will need to calculate the margin of error:

  1. Your chosen confidence interval (1)
  2. The size of the sample you surveyed (2)
  3. The estimated size of the population (3)
  4. The survey result that you're testing (expressed either as a proportion or percentage or as a mean or average)

Note: If you are comparing means, you will also need to know the standard deviation of the mean for both segments.

(1) The confidence interval, almost always in the range of 90 to 99 percent (most often 95%), is used to indicate the reliability of an estimate (in this case the margin of error). For example, a margin of error of +/- 5.0 percent at a 95 percent confidence level can be interpreted to mean that if you were to repeat the survey, 95 out of 100 times the results would come back with the same result within +/- 5.0 points.
(2) Along with the confidence level, the sample size determines the magnitude of the margin of error. A larger sample size produces a smaller margin of error, all else remaining equal.
(3) By population, we mean the larger body of people of interest that is too large to take a census. For example, the population of interest might be all females in Georgia between the ages of 25-50. As a rule of thumb, if a population is more than a couple of hundred people, we can consider it as "infinite" in size for the purpose of the calculator. The calculator can be adjusted for very small size populations (<150).


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