The most accurate of several X2 Approximation Equations used over the years for
calculations involving large degrees of freedom (ν ) is:
3
2
9
2
9
2 1
Χ = − +
ν ν α ν αz
As with all reliability calculations of X2
, we convert the degrees of freedom (ν ) to number
of failures (r) using the equation ν = 2r + 2