Inpernal function: estimate the SD of error terms in the difference model
estimate_sd_error(beta_c, y1, y2, lambda = NA, design_mat_diff)Numeric vector of Step 1 estimates.
Numeric vector of the observed outcome at observation time 1.
Numeric vector of the observed outcome at observation time 2.
The Box-Cox transformation parameter. Default is NA,
indicating no need for a transformation. See Details.
Numeric matrix of the design matrix for difference.
Returns the estimate for sigma_delta if lambda = NULL,
or sigma_delta_lambda on the transformed scale.