Table 1.

Assigning coordinates of ${\mathit{\beta }}_2$ to the respective cohorts and corresponding indicator covariate $\tilde{\mathbf{z}}$

Cohort	Parameter	Dummy
1900–1909	${\beta }_{21}$	${\tilde{z}}_1=1$
1910–1919	${\beta }_{22}$	${\tilde{z}}_2=1$
1920–1929	${\beta }_{23}$	${\tilde{z}}_3=1$
1930–1939	–	Reference cohort
1940–1949	${\beta }_{24}$	${\tilde{z}}_4=1$
1950–1954	${\beta }_{25}$	${\tilde{z}}_5=1$

The cohort 1930–1939, being the largest, acts as reference cohort and therefore possesses no parameter