In general, when you write formal English, it is better not to use abbreviations. In academic writing, it is better practice to say 'for example' than 'e.g.', 'and so forth' than 'etc.' and 'that is' or 'in other words' instead of 'i.e.'. (In footnotes, abbreviations are usual - often of Latin words or phrases.) Think of them as on a par with contractions -
don't use either in academic writing.
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