Comparison of precision across assays. ELISPOT means and SD for each sample were converted to percent of CD8+ T cells using the formula SFC/2.5 × 105/(CD8 percent of PBMC for that donor)×100. This allowed SD to be compared on the same scale. Note that the regression line for ELISPOT (dotted) is consistently higher than the regression line for CFC (dashed) or tetramer (solid). Due to complexity, data points for different donors and different antigens are not distinguished in this Figure; please refer to Figure 2 for relative responses of individual donors and antigens.