Formulas and functions > Functions from A to Z > CONFIDENCE.NORM (confidence interval)

Syntax:

CONFIDENCE.NORM(Alpha, Sigma, n)

Description:

This returns a value that allows you to determine the 1-alpha confidence interval for the population mean of a distribution.

The 1-alpha confidence interval is a range of values around the sample mean x covering the interval from (x - CONFIDENCE) to (x + CONFIDENCE). The probability that this interval contains the population mean is 1-Alpha.

Alpha is the significance level for computing the confidence level. The values must be within the range 0 to 1.

If, for example, Alpha is 5%, the probability that the population mean is outside the confidence interval is 5%. The probability that it is inside is 1-Alpha, i.e., 95%. Thus, 1-alpha is also called the "confidence level".

Sigma is the population standard deviation. It must be > 0.

n is the size of the sample. It must be > 0.

Example:

The average weight of 1000 piglets is to be determined in a pig farm. For this purpose, a sample (with replacement) of the size n=65 is taken. The average weight determined is 30 kg. The standard deviation is 1.6 kg.

The 95% confidence interval (alpha is thus 0.05 here) is now to be determined. Thus, you would calculate as follows:

CONFIDENCE.NORM(0.05, 1.6, 65) returns 0.38897 (kg)

The average weight of the population (of all 1000 piglets) is thus with a probability of 95% between 30-0.38897 kg and 30+0.38897 kg.

Compatibility notes:

Microsoft Excel supports this function only in version 2010 or later. The function is unknown in older versions.