 Welch–Satterthwaite equation

In statistics and uncertainty analysis, the Welch–Satterthwaite equation is used to calculate an approximation to the effective degrees of freedom of a linear combination of independent sample variances, also known as the pooled degrees of freedom, corresponding to the pooled variance.For sample variances , each respectively having degrees of freedom, often one computes the linear combination

where formula_2 is a real positive number, typically formula_3.