Correct spelling for the English word "dd" is [dˌiːdˈiː], [dˌiːdˈiː], [d_ˌiː_d_ˈiː] (IPA phonetic alphabet).
* The statistics data for these misspellings percentages are collected from over 15,411,110 spell check sessions on www.spellchecker.net from Jan 2010 - Jun 2012.