Compute the degrees of freedom according to the original Rubin (1987) approximation.
rubin_orig_df(v_com, var_b, var_t, M)Degrees of freedom according to the original Rubin approximation.
If the between-imputation variance is zero, returns Inf.
Ignored in this function.
Between-imputation sample variance of the point estimates across multiply imputed datasets.
Estimate (according to Rubin's rules) of the variance of the point estimates.
Number of imputations (integer larger than 1).
Let \(V_W = V_T - (1 + 1 / M) V_B\) be the within-imputation variance and \(r = (1 + 1 / M) V_B / V_W\) be the relative increase in variance due to nonresponse. The returned degrees of freedom are \((M - 1) (1 + 1 / r)^2\). Note that the internal computation is algebraically simplified to \((M - 1) ((M V_T) / ((M + 1) V_B))^2\).
Rubin, D.B. (1987). Multiple Imputation for Nonresponse in Surveys. John Wiley & Sons, New York. [Section 3.3]