In our notation: Here p(R m i |Q m j ) refers to the probability that a response R by author i contains marker m given that the quoted post by j also contains m. How much coordination C there is in i's responses to j corresponds to the difference between this conditional probability and the prior probability p(R m i ) for author i, i.e., the probability that any response by i contains a linguistic marker of category m. Given the sparsity of data in online discussion fora with regards to repeated interactions between the same individuals i and j, we compute a score for each Q-R pair (rather than for the set of Q-R pairs between specific authors i and j).
the conditional probability in Equation [1] corresponds to a variable that takes value 1 if both Q and R contain m and 0 if only Q does (and is undefined if Q does not contain m).