Loess Lines of Differential Ability Scales-Second Edition (DAS-II) Copying Ability scores in neurofibromatosis type 1 (NF1) and unaffected sibling groups. Note. The above Loess Lines depict no overlap in DAS-II Copying Ability scores across time, with the unaffected group consistently performing better than the NF1 group. NF1 group sample sizes: 3 years = 11, 4 years = 31, 5 years = 35, 6 years = 30, 7 years = 16, and 8 years = 17. Unaffected sibling group sample sizes: 3 years = 2, 4 years = 17, 5 years = 13, 6 years = 13, 7 years = 10, and 8 years = 8.