Annual population estimates are calculated by updating or “rolling forward” the population from the census base, to account for changes that result from births, deaths and migration. These rolled-forward estimates are subject to accumulating uncertainty over the years until the next decennial census becomes available and the series is re-based again.
Comparison between the mid-2011 Census-based population estimates and the mid-2011 rolled-forward population estimates (for England and Wales) revealed a 464,000 shortfall. This is the difference that has accumulated in the rolled-forward estimates since the 2001 Census provided the base.
Population age and sex structure between mid-2001 and mid-2011
The population pyramid below illustrates the age and sex structure of the England and Wales population in mid-2011. The structure of the pyramid is determined by patterns of births, deaths and migration over previous years. The shaded bars represent the mid-2011 estimates based on the 2011 Census. The black outline represents the age and sex structure of the rolled-forward mid-2011 population estimates, which, when compared to the shaded bars, illustrates the effect of the shortfall on the age and sex structure of the population of England and Wales.
Population pyramid for England & Wales, mid-2011 Census-based estimates (bars) and mid-2011 rolled-forward estimates (line)
Note: The population pyramid stops at age 89, causing the top of the pyramid to be flat.
The age and sex structure of the mid-2011 Census-based estimates is broadly similar to the rolled-forward estimates over the decade. However, there are some key differences:
The number of males in their early to mid-20s were overestimated in the rolled-forward estimates, so the mid-2011 Census-based estimates show fewer males at this age.
The number of females in their late 20s and early 30s were underestimated in the rolled-forward estimates, so more females are shown in the mid-2011 Census-based estimates. This is also the case for males to a lesser extent.
The number of males and females aged 10-19 were underestimated in the rolled-forward estimates, so the mid-2011 Census-based estimates for these ages are accordingly larger.
The number of males and females aged 80 and older were overestimated in the rolled-forward estimates, so the mid-2011 Census-based estimates show fewer people in these ages.
Those aged 64 show a marked difference between the mid-2011 Census-based and rolled-forward estimates.
The proportion of the population aged under 16 was around 20% and the proportion of the population aged 65 and over was around 16% in both the mid-2011 Census-based estimates and the rolled-forward estimates.