Clefts structures show an important asymmetry in interpretation: subject clefts can provide both
corrective or new information foci, while non-subjects (objects, adjuncts) are only corrective.
According to Belletti (2015), such an asymmetry arises from the fact that movement deriving
subject clefts can target two focus positions, but non-subjects can target only one. In both
cases a long-distance dependency is created, triggering locality effects. In this paper, we
show that intervention effects causing ungrammaticality in certain configurations give rise to
lower-than-expected frequencies in corresponding grammatical configurations. Based on sets of
features that play a role in the syntactic computation of locality, we compare the theoretically
expected and the actually observed counts of features in a corpus of thirteen syntactically
annotated treebanks for three languages (English, French, Italian). We find the quantitative
effects predicted by the theory of intervention locality. First, subject clefts, where no intervention
is at play, are more frequent than object clefts, where intervention is at play. Secondly, object
clefts are less frequent than expected in intervention configuration, while subject clefts are
roughly as frequent as expected. Finally, we also find that the differential and direction of
difference between expected and observed counts is directly proportional to the number of
features that establish the intervention, the strength of the intervention. These results provide
a three-fold contribution. First, they extend the empirical evidence in favour of the intervention
theory of locality. Second, they provide theory-driven quantitative evidence, thus extending in a
novel way the sources of evidence used to adjudicate theories. Finally, the paper provides a
blueprint for future theory-driven quantitative investigations.