 Herbert S. Zim, in his classic introductory cryptography text "Codes and Secret Writing", gives the English letter frequency sequence as "ETAON RISHD LFCMU GYPWB VKJXZQ", the most common letter pairs as "TH HE AN RE ER IN ON AT ND ST ES EN OF TE ED OR TI HI AS TO", and the most common doubled letters as "LL EE SS OO TT FF RR NN PP CC".Also, to note that different dialects of a language will also affect a letter's frequency.For example, an author in the United States would produce something in which the letter 'z' is more common than an author in the United Kingdom writing on the same topic