Hand width is measured across the palm at the level of the MCPJ (radial aspect of the second MCPJ to the ulnar aspect of the fifth MCPJ) [Hall et al., 2007]. Caution is advised with the subjective assessment as short metacarpals can mimic a broad palm. In persons with polydactyly that includes a supernumerary metacarpal, that should be separately coded and the measurement technique from Hall et al, [2007] would need to be modified to account for the supernumerary digit (i.e., with postaxial polydactyly, measure to the sixth MCPJ).