Legal marital status
The legal marital status projections are produced
using a component methodology i.e. one based on assumptions
of underlying marriage, remarriage and divorce rates. They
have been produced using the multi-dimensional dynamic projection
model LIPRO developed by the Netherlands Interdisciplinary
Demographic Institute (NIDI). Further details of this package
are available from the NIDI website by clicking here.
The model requires assumptions to be made
for all of the possible transitions between marital statuses.
In addition, assumptions have to be made about the marital
status distribution for both deaths and net migration.
With LIPRO, it is convenient to specify these
assumptions as a function of an initial set of rates. For
these projections, an initial set of marriage, divorce and
(marital status specific) mortality rates by single year
of age and sex has been derived from the 2002-03 components
of change data used by ONS to update the annual population
estimates by marital status. These initial rates were smoothed
to remove any obvious peculiarities in age distributions.
The projections are adjusted within the LIPRO
model to satisfy a number of consistency
constraints. These include internal “two-sex”
constraints (for example, that the number of men marrying
each year must equal the number of women marrying) and the
external constraint that the results of the legal marital
status projection are fully consistent with the results
of the interim 2003-based national (age and sex) projections
for England & Wales.
Cohabitation
As described above, the projections of legal
marital status were produced by a component methodology
i.e. one based on assumptions of underlying marriage and
divorce rates. Ideally, projections of de facto marital
status would be produced by including transitions into and
out of cohabitation within such a model. However, whereas
detailed historical data on transitions between legal marital
status categories are readily available from registration
data, data on cohabitation formation and dissolution is
very limited. Theoretically, estimates could be made from
sample surveys. However, in practice, the data is not of
sufficient quality for this purpose. In particular, sample
sizes are far too small to produce reliable data for individual
ages. As the model used for the legal projections is a dynamic
model, assumptions made about cohabitation transitions would
effect the results for legal marital status. It would therefore
be likely that the inclusion of necessarily speculative
data on cohabitation would actually reduce the quality of
the legal marital status projections.
Instead, assumptions have been made about
the proportions cohabiting in each age/sex/legal marital
status group and these have been applied to the results
of the legal marital status projections.
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