Government’s decision to use an amended population estimate to determine the number of COVID vaccinations needed to reopen the border has drawn controversy, and raised questions over how it was calculated.
Now, in response to a Freedom of Information request by the Cayman Compass, the Ministry of Finance & Economic Development has made internal records available showing how and why the population estimates were amended.
The move to amend the population estimate, announced at a press conference on 16 June, increased Cayman’s estimated population by about 8%, from 65,786 to 71,106.
That had the effect of pushing the 80% ‘full vaccination’ target for Cayman’s population, which had appeared to be within reach, months into the future.
It still remains difficult to attain.
At this stage, 50,682 residents have received at least one vaccine jab. This is approximately 6,200 people less than the number required to reach 80% under the revised population figures.
The ministry said in its FOI response that Cayman’s population had “changed immensely” since the last Census in 2010, and had also changed considerably since the last Labour Force Survey (LFS) in the fall of 2020.
During a verbal discussion on 26 May with the Economics and Statistics Office (ESO), the newly-elected government asked the ESO to validate the published population estimate of 65,786 from October 2020 and estimate the population for April 2021.
The ESO prepared a draft report for internal purposes, which pointed out that the estimated population from the Labour Force Survey contained a 5% margin of error, stating the statistics office is 95% confident the number of residents could be between 60,886 and 70,686.
The ESO recommended government should use the upper limit of 70,686 to calculate vaccination ratios.
This figure was then updated based on records of births and deaths, changes in work permits and permanent resident grants, and net migration of Caymanians, resulting in the maximum upper population limit of 71,106 now used to calculate vaccination ratios and targets.
The ESO also validated the age bands of the population. These are not normally estimated, but were last determined during the 2010 census.
The report adjusted the census data by 11 years for Caymanians, to account for the time that has past since 2010, and applied the figures from birth and death records. It also updated the age bands for non-Caymanians with current work permit and permanent residency data, including dependants.
This resulted in a lower share of the population of under 12-year-olds (12.7%) and a larger share of over 60s (12.2%) than if the age band percentages of the 2010 census had been applied to current estimates of Cayman’s total population.
EDITOR’S NOTE: In this case, the 5% margin of error refers to the number of times the population figure is expected to be larger or smaller than the given range (i.e., 1 in 20 times), not the size of the range (such as plus or minus 5%). The range of the estimate depends on the population mean, the standard deviation and a specific score (the z-score) related to the chosen confidence interval (in this case 95%). If a smaller margin of error is selected, the range of the population estimate would be wider.