Solution (using degrees of freedom = n – 1 = 29) and t α/2 = 2. Construct a 95% confidence interval estimate for the population mean. The sample mean (x̄) was $1,500, with a sample standard deviation of $89.55. Thirty people from a population of 300 were asked how much they had in savings. Or, for a confidence interval for a mean and unknown population standard deviation, the formula (with FPC) is: For example, the standard error of the mean formula is: The following table of values shows how the FPC decreases for a population of 10,000 as the sample size gets larger:īasically, place the correction at the end of the formula you want to use. As the sample size falls under 5%, the value becomes somewhat insignificant (an FPC is. If the calculated value for the FPC is close to 1, it can be ignored. Note: A downside of using the FPC is that it can cause uncertainty when applying the results to a larger population, so you should be careful when making inferences. For example, you might perform a telephone survey of 10,000 people once a person has been called, they won’t be called again. Most real-life surveys involve finite populations sampled without replacement.
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