1. A method for determining threshold voltage shift in memory cells, comprising: determining changes in threshold voltage for memory cells at a first data state by searching threshold voltage data of memory cells programmed to the first data state having threshold voltages within a first range of threshold voltages; and determining changes in threshold voltage for memory cells at a second data state by searching threshold voltage data of memory cells programmed to the second data state having threshold voltages within a second range of threshold voltages, wherein the second range is shifted from a previous range based on the changes in threshold voltage for memory cells programmed to the first data state, wherein the first data state is different than the second data state.