Vaccine coverage and denominators II
What is the vaccine coverage by age groups in England?
On 9th September, Public Health England published a vaccine surveillance report. Robert Peston, the ITV political editor, highlighted statistics about unvaccinated case rates.
The concern was the population denominator in England, affecting interpretations of case rates. Many people covered this issue, including James Ward, Colin Angus, and BBC’s More and Less. Last Sunday, I co-wrote a short column in The Observer with David Spiegelhalter.
What is the statistical issue?
The problem is we do not know how many people there are in England. Since we count the number of vaccinated people, the rest are not vaccinated.
There are major differences between two different sources of population figures. The Office for National Statistics produces mid-year population estimates. These figures take last decade’s census and age the population. Statisticians then add births, remove registered deaths, and apply migration estimates.
The effect of migration is uncertain. In previous years, the main source was the International Passenger Survey. Using a survey to track migration meant high uncertainty in those estimates. Due to the pandemic, that survey halted. In…
