rivista italiana di economia demografia e statistica - Sieds

36
Volume LXIII nn. 3-4 – Luglio-Dicembre 2009
The other explanatories considered are macrocohort dummies from X 8 to
X 17 , and month dummies from X 18 to X 28 . We can observe that almost all
macrocohort dummies coefficients are significant, especially we can notice that the
absolute value is larger for younger and older macrocohorts. X 0 is a constant
adjusted for heteroschedasticity.
Table 1 – Estimates.
Socio-demographic variables
Macrocohort and month dummies
Est.
Std. t - t -
Std. t - t -
Est.
Err value prob
Err value prob
X0 7.81 0.05 154.43 < 0.001 *** X8 -0.46 0.04 -10.9 < 0.001 ***
X1 -0.6 0.17 -3.55 0 *** X9 0.01 0.02 0.38 0.71
X2 -0.17 0.08 -2.3 0.02 * X10 -0.01 0.02 -0.38 0.71
X3 -0.18 0.07 -2.52 0.01 * X11 -0.07 0.02 -3.16 0 **
X4 -0.24 0.02 -9.64 < 0.001 *** X12 -0.08 0.03 -3.14 0 **
X5 -0.06 0.02 -3.25 0 ** X13 -0.1 0.03 -2.8 0.01 **
X6 0.33 0.07 5.01 0 *** X14 -0.13 0.04 -3.38 0 ***
X7 0.86 0.09 9.17 < 0.001 *** X15 -0.2 0.04 -4.77 0 ***
X16 -0.3 0.04 -6.92 0 ***
X17 -0.38 0.04 -8.96 < 0.001 ***
X18 -0.01 0.01 -1.17 0.24
X19 0 0.01 0.02 0.99
The regression results are then used to compute the contributions from
occupation, education and demographic variables to income inequality. In Figure 1
we represent the contributions in the first round. Focusing our attention on the
occupation effects, we notice that this factor explains the income inequality for
macrocohorts from 1 to 8, i.e. for individuals aged 20-60, this means that
occupation affects income distribution during the working age, as expected. The
demographic characteristics seem to be relevant for macrocohorts from 1 to 5, this
is due to the number of children aged 0-14 in the household as explanatory
variable. Looking at the education effect we can notice that the contribution to
income inequality is higher for individuals aged 20-34 and individuals aged 40-45.
The first peak can be interpreted as the effect of individuals that enter early in the
labor market with secondary education. As for the second peak it can be related to
the big time of career for individuals with higher education.
The estimates of the second round contributions are shown in Figure 2. We can