When you think about leisure in the utility function, for most applications you need to take a stand on some properties: is the income effect larger than the substitution effect? Is leisure a normal good in the first place? Convincing empirical evidence is surprisingly difficult to find: read the endless debate between microeconomists and macroeconomists about the size of the wage elasticity. This may be an aggregation issue, but maybe we are lacking a clear natural experiment.
Naci Mocan and Duha Altindag report on an interesting change in the way members are paid in the European parliament. Whereas previously they were compensated at wildly different levels by there home countries, since July 2009 they get money according to a uniform rule: 38.5% of a European judge's salary as a base, plus a per diem when present. Mocan and Altindag then use the difference between and with the previous schemes to highlight that an increase in the base reduces attendance (yes, the income effect! Leisure is normal!) and an increase in the per diem increases attendance (the substitution effect is larger than the income effect). Politicians are rational after all.