CONFIDENCE

Syntax: **CONFIDENCE( Alpha, SDev, N)**

*Alpha* = significance level

*SDev* = standard deviation

*N* = sample size

**CONFIDENCE** returns the two-sided *Alpha - 1*
confidence interval for the mean of a normally distributed
population with a standard deviation of *SDev* given
a sample size of *N*. *Alpha* must be greater than
zero and less than one. *SDev* must be greater than zero.
*N* must be an integer value greater than zero. If *N*
is not an integer, it is truncated such that the fractional
portion is removed; i.e., an *N* value of 10.9 will be treated
as 10.

**Example:**

Suppose A1..A50 contains 50 samples of a random variable with
a computed average of 14.73 and standard deviation of 1.19;
i.e., **AVERAGE**(A1..A50) = 14.73 and **STDEV**(A1..A50)
= 1.19. Then the 95% confidence interval for the mean of the
population from which the samples were taken is given by:

**CONFIDENCE**(0.05, 1.19, 50) = 0.32984511

Therefore, the 95% confidence interval is 14.73 plus or minus 0.32984511, which is 14.400155 to 15.059845.

**Excel function:** CONFIDENCE

Grey Trout Software

02 March 2003