Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The oligo(dT)-precipitation was performed essentially as described in Baltz et al. (2012) with the following modifications: The number of washing steps was increased (4√ó with lysis/ binding buffer and 6√ó with NP40 washing buffer [50 mM Tris
 HCl, pH 7.5, 140 mM LiCl, 2 mM EDTA, pH 8.0, 0.5% NP40,‚Ä¶
Category: