Single-cell measurements preserve crucial information that is lost by bulk genomics assays. (A) Simpson's Paradox describes the misleading effects that arise when averaging signals from multiple individuals. (B) Bulk measurements cannot distinguish changes due to gene regulation from those that arise due to shifts in the ratio of different cell types in a mixed sample. (C) Time series experiments are affected by averaging when cells proceed through a biological process in an unsynchronized manner. A single time point may contain cells from different stages in the process, obscuring the dynamics of relevant genes. Reordering the cells in “pseudotime” according to biological progress eliminates averaging and recovers the true signal in expression (Trapnell et al. 2014).
