Analysis of correlation between TPO threshold of individual CD34⁺CD41⁺ progenitors and clone size achieved, expressed as NbD_r. Samples of 500 TPO thresholds (□) have been simulated so that the corresponding TPO₅₀ and coefficients of variation were those in Table 1. The 4 horizontal groupings represent the sets of simulated values obtained for the 4 NbD size classes, from top to bottom: 8 to 15 MKs; 4 to 7 MKs; 2 to 3 MKs; and 1 MK. Solid and dashed lines indicate the regression line through the total set of points and through percentiles 2.5% and 97.5% of each of the 4 sets of simulated TPO threshold values, respectively. R² is the squared Spearman rank order correlation (P < .001).