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 following methods were introduced in order to include structural 3D information in QSARs/QSPRs: CoMFA comparative molecular field analysis and its variants CoMSIA (MSIA - molecular similarity indices Analysis) [23]; ▪ WHIM - weighted holistic invariant molecular (and its variant MS-WHIM - molecular surface WHIM) [24];▪ MTD minimal topological distance (and its variant MSD, S - steric) [25]; ▪ FPIF - fragmental property index family [26]; ▪ MDF - molecular descriptors family [27]; ▪ MDFV - molecular descriptors family on vertices [28-30]; ▪ TOPS-MODE topological sub-structural molecular design [31-35], ▪ other approaches [36-39].
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