Editing Allan variance (section)

===Effective degrees of freedom===
The [[Degrees of freedom (statistics)|degrees of freedom]] represents the number of free variables capable of contributing to the estimate. Depending on the estimator and noise type, the effective degrees of freedom varies. Estimator formulas depending on ''N'' (number of total sample points) and ''n'' (integer multiple of ''&tau;''<sub>0</sub>) has been found empirically:<ref name=Howe1981/>
:{| class="wikitable"
|+ Allan variance degrees of freedom
|-
!Noise type
!degrees of freedom
|-
|white phase modulation (WPM)
|<math>\text{df} \cong \frac{(N + 1)(N - 2n)}{2(N - n)}</math>
|-
|flicker phase modulation (FPM)
|<math>\text{df} \cong \exp\left[\left(\ln \frac{N - 1}{2n} \ln \frac{(2n + 1)(N - 1)}{4}\right)^{-1/2}\right]</math>
|-
|white frequency modulation (WFM)
|<math>\text{df} \cong \left[ \frac{3(N - 1)}{2n} - \frac{2(N - 2)}{N}\right] \frac{4n^2}{4n^2 + 5}</math>
|-
|flicker frequency modulation (FFM)
|<math>\text{df} \cong \begin{cases}\frac{2(N - 2)}{2.3N - 4.9} & n = 1 \\ \frac{5N^2}{4n(N + 3n)} & n \ge 2\end{cases}</math>
|-
|random-walk frequency modulation (RWFM)
|<math>\text{df} \cong \frac{N - 2}{n}\frac{(N - 1)^2 - 3n(N - 1) + 4n^2}{(N - 3)^2}</math>
|}