This calculator will determine the confidence interval for a chosen confidence level given a study’s sample size and a mean and standard deviation response to a survey. This calculator tests means. To test a proportion, use the Confidence Interval for Proportions calculator.
Step 1 Select desired confidence level:   %
Step 2 Enter sample size:
Enter number of interviews completed
 
Step 3 Enter observed mean:
Enter a number
 
Step 4 Enter observed standard deviation:
Enter a number
 
RESULT Confidence interval:
Click the Calculate button
  Range for true population mean:      to   
  Reset Form Calculate Form

What the results mean

When you are interviewing a sample of respondents drawn from a population, the mean value you obtain at a certain question may be different from the mean value you would obtain if all members of the population where interviewed (true population mean). There is some likelihood, called the confidence level, that the true population mean falls within a particular range, called the confidence interval, around the mean value you obtained from your sample.

For example, if you interview 500 people, and obtain a mean value to a question of 25.0 with a standard deviation of 12.5, and you desire your confidence level to be 95%, the corresponding confidence interval is 1.1. That is to say that you are 95% certain that the true population mean falls into the range from 23.9 to 26.1.

 

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