Distribution of disease severity score in 1 validation test set. Each box plot displays the observations between the first and the third quartile in the rectangle, with a line for the median. The whiskers extend to 1.5 times the interquartile range from each end of the rectangle. Circles represent outliers beyond the end of the whiskers. Box plots in blue display the score distribution for patients who died, and box plots in red display the score distribution for survivors. There is a separation between the scores of subjects in these groups that is especially clear in patients aged 18 to 40 years (B). In the group aged 2 to 18 years (A), 2 subjects with a score below 0.5 died. Both subjects (1 HbSC, score 0.01; 1 with sickle cell anemia, score 0.24) died for unknown causes. In the group aged 18 to 40 years (B), 2 of the 4 subjects with low severity score died for unknown causes as did 2 of the 3 subjects with low severity score in the group aged older than 40 years (C). Many young subjects with a high severity score survived until the end of the follow-up, consistent with the high survival rate of children even with a severe clinical profile.