log-log plots of FDR versus the maximum spike-in concentration at varying levels of fold change (FC). The dashed line in each plot is the log FDR value corresponding to q = 0.05. Plots for higher fold changes are available at our web site. (a) FC = 2. (b) FC = 4. (c) FC = 8. (d) FC = 16. Due to the precision of the Matlab routines used for this study, log FDR values below -16 were cut off at -16.