Structural analysis further classified LBs into five categories: article-headed (e.g., "a lot of," "a matter of"), preposition-headed (e.g., "as long as," "in order to"), noun-headed (e.g., "part of the," "members of the"), verb-headed (e.g., "to ensure that," "is going to"), and pronoun-headed (e.g., "he said that," "it will be").
The preposition-headed category was found to be the most productive, with "in" and "as" dominating. However there is a difference between Corpora NMD (78%) and BNC (22%)