In reply to Mike C.

I'm glad you mentioned this! The value of a Scrabble tile was chosen to reflect how common/rare the letter is in English usage. However, in Scrabble you can make any word in a dictionary, whereas the corpus frequencies reflect how words are actually used in written text. For example, T, H, and E get used a lot in written English because the word 'the' is very common. Thus the distribution of letters in a dictionary (where every word appears once) is different from the distribution in a corpus (where common words are repeated many times).