The CONFIDENCE() function returns a value that togehter with the mean of a poulation can be used to find the confidence interval of a range of data values.. The syntax for the function is CONFIDENCE (alpha, standard_dev, size ). The arguments "alpha","standard_dev" and "size" can be a numbers, or referenced cells or a named range. However referenced cells that do not contain values or that cannot be converted to numeric values such as text, logical values return a #VALUE error. Note: Values in the "alpha" argument must be between 0 and 1 otherwise the function will return a #NUM error. If the "standard_dev" value is less than or equal to 0 or the argument "size" is less than 1 the function will return a #NUM error value. The CONFIDENCE function is used to calculate an estimeated range of values which are likely to include an unknown population parameter (data point). This is done by setting a significance value "alpha" (which gives the desired level of confidence) entering the known standard deviation of a population "standard_dev" and the the number of data points in the population sample "size". Note: Confidence value = 100*(1-alpha)% where the value alpha is the significance level. For example an alpha of 0.03 gives a 97% confidence level. With these values the CONFIDENCE function then calcualtes the confidence range above and below the mean population value. For example: CONFIDENCE(0.05, 2.5, 50) = 0.692952 The confidence interval is the mean plus or minus this result. ie. 30 ± 0.692952 It is this confidence interval between approximately 29.3 and 30.7 that we can be 95% confident that any samples taken from the population will have a mean value of 30 and conversely a sample taken that has a mean value larger than 30.7 or smaller than 29.3 has only a 5% chance of occuring.

How to use the CONFIDENCE() function: Type " =CONFIDENCE( " Enter the coordinate of the "Significance value" data cell "A2" Type a comma. Enter the coordinate of the "Standard deviation" data cell "B2". Type a comma. Enter the coordinate of the "Population size" data cell "C2". Type ")" then press the "Enter" key.