A method is provided for altering distribution of a chosen characteristic of a plurality of memory cells forming a memory device. The method comprises identifying a subset of the memory cells whose value of the chosen characteristic is within a predetermined end region of the distribution, and then performing a burn-in process during which one or more operating parameters of the memory device are set to induce aging of the memory cells. During the burn-in process, for each memory cell in the subset, the value stored in that memory cell is fixed to a selected value which exposes that memory cell to a stress condition. In contrast, for each memory cell not in the subset, the value stored in that memory cell is alternated during the burn-in process in order to alleviate exposure of that memory cell to the stress condition. Such an approach allows a tightening of the distribution of the chosen characteristic, thus improving the worst case memory cells.