The correlation between age at first diagnosis and parental education level. Box plots show the age at first diagnosis grouped by maternal education level and paternal education level. The thick band inside the box is the median, and the bottom and top of the box are the first quantile (Q1) and the third quantile (Q3). The ends of the whiskers represents data within 1.5 *interquartile range (IQR) from the lower quantile (Q1) or the upper quantile (Q3), where IQR is equal to Q3 minus Q1. The fitted simple linear regression lines are highlighted in different colors (maternal orange line: slope = -6.7e-02 (95% confidence interval (CI): -1e-01 to -3.3e-02), P value = 1.3e-04, paternal blue line: slope = -4.9e-02 (95% CI: -8.2e-02 to -1.6e-02), P value = 3.9e-03). Abbreviations: M, middle school or lower; H, high school; J, junior college; R, regular college; G, graduate.