Calculate the confidence interval for a sample mean, given the standard deviation, sample size, and desired confidence level.
A confidence interval gives a range of values likely to contain the true population mean, based on a sample.
The margin of error equals the Z-score times the standard deviation divided by the square root of the sample size. The interval is the sample mean plus or minus the margin of error.
Enter the sample mean, standard deviation, sample size, and select your confidence level, then click Calculate.
Example: A sample mean of 50 with standard deviation 8 and sample size 40 at 95% confidence gives an interval of approximately 47.52 to 52.48.
What does 95% confidence mean. It means that if the sampling were repeated many times, about 95% of the calculated intervals would contain the true population mean.
Does a larger sample reduce the margin of error. Yes, increasing the sample size decreases the margin of error and narrows the interval.