To my eye, they did an
excellent and comprehensive job scanning the research
literature to find any eligible studies, culling the ones lacking the sufficient methodological chops, and
then coding each as to whether they found impacts that were statistically significantly positive, insignificantly positive, insignificantly negative, or significantly negative.
I was able to combine public law with
literature by reading John Buchan's The 39 Steps and
then William J. Galbraith's
excellent biography of our literary GG, John Buchan: Model Governor General.