When wage rate changes, income effect and substitution effect
on leisure reinforce each other.
That is, if leisure is an inferior good, then income effect
will reinforce substitution effect as people will demand less
leisure when income Increases or in other words higher wage will
encourage people to work more.
Similarly if leisure is a normal good, then an increase in
income will cause the demand for leisure to increase and the demand
for work to decrease.
In this way both substitution and income effects reinforce each
other on leisure.