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<< Click to Display Table of Contents >> CONFIDENCE (confidence interval) |
Note: CONFIDENCE is supplemented by the new identical function CONFIDENCE.NORM, which is available in newer versions of Microsoft Excel (2010 or later).
Syntax:
CONFIDENCE(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(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.
See also: