Here the precision of MaltParser and MSTParser is very different, with MaltParser being more precise for arcs nearer to the leaves, but less precise for those nearer to the root. One possible reason is that arcs near the bottom of the tree require comparatively fewer shift-reduce actions to build, and are therefore less prone to the propagation of search errors. Another important reason, as pointed out by<cite> McDonald and Nivre (2007)</cite> , is the default single-root mechanism by MaltParser: all words that have not been attached as a modifier when the shift-reduce process finishes are attached as modifiers to the pseudo-root.