Sociolinguistics 1, Exercise 2: the ING variable

Variable: ING.
Variants: -ing and -in' (the source's own wording: "-ing vs. -in'").

Principle of Accountability (as Wikipedia gives it, citing Tagliamonte):
count the tokens of a variant against the number of times it could have
occurred. For ING, count how many times a speaker says -in' out of all the
words where either -ing or -in' could have been said, not just how many
-in' you notice. Without the total, a high count of one variant may only
mean the speaker said many such words.