Library 2 shows biases similar to but weaker than those of library 1. ln (ORobs) from library 1 was plotted versus ln (ORobs) from library 2 for each amino acid (A) or for groups of amino acids (B). Hydrophobic residues were defined as Phe, Ile, Leu, Met, and Val. Polar amino acids were defined as Ser, Thr, His, Gln, and Asn. Charged amino acids are Asp, Glu, Lys, and Arg. Aromatic amino acids were defined as Trp, Tyr, and Phe. Error bars represent 95% confidence intervals.