The Dark Triad across academic majors?

In general, I am skeptical of such results and their typical interpretations, still economics plays a role in this paper and perhaps it is worth at least a casual ponder:

The Dark Triad traits (i.e., narcissism, psychopathy, and Machiavellianism) have been associated with the desire for power, status, and social dominance in the workplace, and these desires have been hypothesized to draw Dark Triad individuals towards occupations affording such outcomes. Following this reasoning, the Dark Triad may also influence educational choices. Research in other personality traits has shown that Big Five traits impact educational choices: Students in different academic majors differ on Big Five traits at enrollment. The aim of the present study was to explore whether there are also pre-existing Dark Triad differences across academic majors. Accordingly, the Big Five and the Dark Triad traits were measured in a sample of newly enrolled students (N = 487) in different academic majors (psychology, economics/business, law, and political science), and mean scores were compared. Group differences in the Big Five personality traits largely replicated previous findings. Group differences in the Dark Triad traits were also found and included medium and large effect sizes with the largest differences being between economics/business students (having high Dark Triad scores) and psychology students (having low Dark Triad scores). These findings indicate that Dark Triad as well as Big Five traits may influence educational choices.

That is from Anna Vedel and Dorthe K. Thomsen, via Rolf Degen.

So which group is more rational?