Horn, E., & Ashbaugh, E. J. (1928). The Horn-Ashbaugh high school speller: Incorporating the findings of a tabular analysis of 5,100,000 words of ordinary writing and of over 1,000,000 running words of letters written by high school students. J.B. Lippincott Co.

Horn, Ernest, and Ernest J. Ashbaugh. The Horn-Ashbaugh High School Speller: Incorporating the Findings of a Tabular Analysis of 5,100,000 Words of Ordinary Writing and of over 1,000,000 Running Words of Letters Written by High School Students. Philadelphia [etc.]: J.B. Lippincott Co, 1928.

Horn, Ernest, and Ernest J. Ashbaugh. The Horn-Ashbaugh High School Speller: Incorporating the Findings of a Tabular Analysis of 5,100,000 Words of Ordinary Writing and of over 1,000,000 Running Words of Letters Written by High School Students. J.B. Lippincott Co, 1928.