Shifting cell voltage based on grouping of solid-state, non-volatile memory cells

Cells of a solid-state, non-volatile memory are assigned to one of a plurality of groups. Each group is defined by expected symbols stored in the cells in view of actual symbols read from the cells. Based on cell counts within the groups, it can be determined that a shift in a reference voltage will reduce a collective bit error rate of the cells. The shift can be applied to data access operations affecting the cells.