Finding Sample Size With Confidence Interval. There are three factors that determine the size of the confidence interval for a given confidence level. Formula For confidence intervals for proportions the following formula is used CI sample proportion - MoE MoE z-value x square_root pqn x FPM where p is the proportion of interest in the sample and q 1 p and n is the sample size.
Confidence Intervals and Sample Size. Choose the required confidence level from the dropdown menu Input the margin of error Input the proportion of the total population. If the population standard deviation cannot be used then the sample standard deviation s can be used when the sample size is greater than 30.
Use the sample size formula Plug in your Z-score standard of deviation and confidence interval into the sample size calculator or use this sample size formula to work it out yourself.
Determine the confidence level. You can find a distribution that matches the shape of your data and use that distribution to calculate the confidence interval. If the population standard deviation cannot be used then the sample standard deviation s can be used when the sample size is greater than 30. The difference was the sample size.
