Returns the inverse of the onetailed probability of the chisquared distribution. If probability = CHIDIST(x,...), then CHIINV(probability,...) = x. Use this function to compare observed results with expected ones in order to decide whether your original hypothesis is valid.
Syntax
CHIINV(probability,degrees_freedom)
Probability is a probability associated with the chisquared distribution.
Degrees_freedom is the number of degrees of freedom.
Remarks
 If either argument is nonnumeric, CHIINV returns the #VALUE! error value.
 If probability < 0 or probability > 1, CHIINV returns the #NUM! error value.
 If degrees_freedom is not an integer, it is truncated.
 If degrees_freedom < 1 or degrees_freedom > 10^10, CHIINV returns the #NUM! error value.
Given a value for probability, CHIINV seeks that value x such that CHIDIST(x, degrees_freedom) = probability. Thus, precision of CHIINV depends on precision of CHIDIST. CHIINV uses an iterative search technique. If the search has not converged after 100 iterations, the function returns the #N/A error value.
Example
The example may be easier to understand if you copy it to a blank worksheet.
How to copy an example
 Create a blank workbook or worksheet.
 Select the example in the Help topic.
Note Do not select the row or column headers.
Selecting an example from Help
 Press CTRL+C.
 In the worksheet, select cell A1, and press CTRL+V.
 To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.

A 
B 
Data 
Description 
0.050001 
Probability associated with the chisquared distribution 
10 
Degrees of freedom 
Formula 
Description (Result) 
=CHIINV(A2,A3) 
Inverse of the onetailed probability of the chisquared distribution (18.3069735) 
