It has long been suspected by one of us (A. C. C.) that the combined diagnoses of pernicious anemia and vitiligo occurred in a greater than statistically expected concurrence. To substantiate this observation a survey of patients with either or both diseases was made. Of 801,678 admissions to the University of Michigan Hospital from 1934 through 1954 there were 1398 patients diagnosed as having pernicious anemia, 531 as vitiligo, and 22 patients with the combined diagnosis. Pernicious anemia was present in 0.17% of the patients admitted and 0.066% had vitiligo. Arithmetically then 1.6% of the patients with pernicious anemia had vitiligo and 4.1% of the patients with vitiligo had pernicious anemia (Table).
To calculate the theoretical occurrence of the combined diagnoses the formula NP1P2 was used. N equals the total number of patients observed (801,670), P1 equals the frequency of occurrence of patients