The detection of expressed genes in a population-based measurement (left) can be the result of many possible scenarios (right): all cells might have an equal amount of the transcripts (top), some cells might express a given gene while others do not (middle), and/or there can be grades of expression between different cells (bottom). Direct analysis of single cells, as approached by Nestorowa et al, is the only way to deconvolute which of these scenarios are present.