"Association" is pronounced as either
/əˌsəʊsiˈeɪʃ(ə)n/
Or
/əˌsoʊʃiˈeɪʃən/
What I am focusing on in this example is the middle sound /ʃ/ -sh- which is made with ⟨ci⟩. Something came to my mind that there might be a rule in English which says that If a word has different pronunciations, the one which is made by different letters (here ⟨ci⟩) is preferred to other pronunciations which use a sound made by fewer letters (here /s/ made by ⟨c⟩ alone).
There are similar rules in other languages; for example in Arabic, if two words are synonyms the one with more letters is the preferred choice.