In order to provide the overall value of ARI, we follow the addition approach used in (Lopukhin et al., 2017).
since the quality measure is computed for each lemma individually, the total value is a weighted sum, namely where w is the lemma, I(w) is the set of the instances for the lemma w, ARI w is the adjusted Rand index computed for the lemma w. the contribution of each lemma to the total score is proportional to the number of instances of this lemma.