(a,b) The fraction of distinct cfDNA molecules that have the same start/end positions and the same barcodes (i.e., barcode collisions) is shown for two clinically obtainable quantities of recovered hGEs from the same 32ng normal donor sample. Barcode collisions were predicted based on the number of molecules with identical start/end coordinates and the number of possible physical UIDs (=256). (c) Estimated percentages of unambiguously barcoded molecules, pooled from results in a,b. (d) Percentage of uniquely barcoded molecules in a,b calculated using an approach that counts collisions within UID families containing heterozygous SNPs. Data are presented as means +/− 95% confidence intervals, and are shown for 2,100 and 4,000 recovered hGEs across 169 and 153 heterozygous SNPs with adequate coverage (>50% of the median depth), respectively. Additional details are provided in Supplementary Note.