The left table column contains each letter of the alphabet ordered by the
frequency it occurred. The right column contains the most common English
digraphs ordered by occurrence. Both columns are from a sample of 40,000
different English words.
This information is from a Cornell University’s Math Explorers’ Club
(supported partly by the National Science Foundation). No further
information is available on how these were calculated generated, but it
corresponds closely with several cryptography textbooks I own.