Amino acid propensities for each SCOP fold. Box plots of amino acid propensities for each SCOP fold for α-helices (A) and β-strands (B). Each box encloses 50% of the data with the median value displayed as a line. The top and bottom of the box mark the limits of ±25% of the data. The lines extending from the top and bottom of each box mark the minimum and maximum values within the data set that fall within an acceptable range. Any value outside of this range, called an outlier, is displayed as an individual point. Underlining of certain residues (one-letter code) on the horizontal axis denotes that the results from the Fisher-Irwin population proportion test indicated that differences in propensities are statistically significant between folds.