pooledVariance

Computes the pooled variance when combining samples from the same population. The pooling process assumes a weighted average of the variances. In the case where each estimate only has count equal to 1, the variance is computed from the two data points. In the cases where the pooled sample will have 3 elements, the variance associated with the sample size of 2 is used. In the cases where both samples have 2 or more elements, a weighted pooled variance is computed.