Second, data selection mostly targets sequences very far from the target syntax: sentences that only disrespect a local preference of child position are less fluent, and consequently have a lower rank, than their hypothetical counterpart with switched positions; but they are not ungrammatical enough to be pushed into the 10% worst territory.
the data transformation approach is not restricted to preexisting n-grams, and it directly confronts the given sequence with its counterpart to keep only the most fluent, thus acknowledging local preferences.