Question

What are the 95% confidence limits for a control mean of 140 mg/dL and a standard deviation (s) of 2.5 mg/dL?

Answer 1

The formula for calculating 95% confidence limits is shown below.

95% confidence limits = mean ± {t * (s/(n)^1/2)}

Where 'n' is the sample size.

In general, the t-value for 95% confidence interval for large sample size = 1.96

For simple example, consider n = 36

Then 95% confidence limits = 140 ± {1.96 * (2.5/(36)^1/2)}

i.e. 95% confidence limits = 140 ± 0.81667

i.e. 95% confidence limits = [139.18333, 140.81667]

Note: The values change according to the sample size.