For the independent-measures t test, which of the following describes the estimated standard error of the difference in sample means (whose symbol is )? The difference between the standard deviations of the two samples An estimate of the standard distance between the difference in sample means (M₁ – M₂) and the difference in the corresponding population means (μ₁ – μ₂) A weighted average of the two sample variances (weighted by the sample sizes) The variance across all the data values when both samples are pooled together