Stats using excel

excel-stats.txt

Returns a confidence interval.
Syntax:

CONFIDENCE(α; sd; size)

    sd (> 0) is the (known) standard deviation of a normal distribution. 

    size is the size of a sample from that distribution. 

    α is the significance level (0 < α < 1), which determines the desired confidence level = (1 - α)*100%. 
    Thus for example α = 0.05 gives a 95% confidence level. 

    CONFIDENCE returns a value that when added and subtracted from the sample mean gives an interval within 
    which the population mean is expected to lie with the specified confidence level. 

    CONFIDENCE calculates NORMINV(1 - α/2; 0; 1) * sd / √(size) 

Example:

CONFIDENCE(0.05;1;20)

    returns approximately 0.438. With a 95% confidence level, the mean of the entire population lies within ±0.438 
    of the sample mean.