Hypothetical distribution of HbF/F-cell and the percent F-cells in a patient with 30% HbF. Data were generated as in Figure 1, using a β distribution with fixed mean = 10 and decreasing standard deviation. The left panel shows an extreme example of U-shaped distribution with a mean of 10 pg but very large variance. In this situation, the F-cells are either totally protected (100% HbF) or totally unprotected (0% HbF), with very few cells with intermediate concentrations of HbF/F-cell.