Last updated October 2, 2013.[br][br]The formula below computes the sample size needed to estimate[br]the population mean within a given margin of error and at a given [br]confidence level.[br][br]Move the sliders to change the values of the population standard [br]deviation σ , the margin of error E, and the confidence.[br][br]How does the sample size change as the standard deviation changes?[br]How does the sample size change as the margin of error changes?[br]How does the sample size change as the confidence changes?

The value z α/2 is the standard score corresponding to [br]an area of α/2 in the right tail of the normal distribution. [br]If the confidence is converted to a decimal value C, then [br]α = 1 - C. For example, if the confidence level is 98%, [br]then C = 0.95 and α = 1 - 0.98 = 0.02.