There were only 17 students in the Duke Math cohort, representing the # of math majors who received financial aid during the two-year measurement period. As @Mwfan1921 commented above, limited database, so salary data cannot be accessed for many majors as too few students on financial aid graduated with that major.
My son was a math major, but I cannot look up earnings for his school because of the inadequate sample size. It would be interesting to see the distribution of salary points.