GSAS_USE addresses the effects of systematic errors in Rietveld refinements. The errors are categorized into multiplicative, additive, and peak-shape types. Corrections for these errors are incorporated into using a Bayesian statistics approach, with the corrections themselves treated as nuisance parameters and marginalized out of the analysis. Structural parameters refined using the proposed method represent probability-weighted averages over all possible error corrections.
Gagin, A. & Levin, I., Accounting for Unknown Systematic Errors in Rietveld Refinements: A Bayesian Statistics Approach. J. Appl. Cryst. 48, 1201-1211, (2015).