Population Projections

This Bulletin provides a summary of the population projections produced using the dataset from the 2016 Population & Housing Census (the census was conducted in February 2016, and a summary report and a set of tables detailing the results are available). To accompany this Bulletin, a detailed dataset is available.

Population projections help understand the size and structure of the future population, and are a useful input for planning and managing St Helena’s development. But it is important to bear in mind that these projections are the result of a number of assumptions about the future patterns of growth in St Helena’s population. Small changes in the actual fertility, mortality and migration patterns may have quite large impacts on the size of different groups of the population. For this reason, population projections are not predictions; rather, they show how St Helena’s population would evolve if the assumptions that are made were to hold true.

Summary Results

Table 1 provides key results from projections made under three different assumptions of migration: no migration (no immigration or emigration); a low immigration model from observed patterns in 2014/15 (model 1); and a higher immigration model from observed patterns between 2010 and 2016 (model 2). In all cases, assumptions about fertility and mortality are the same and are based on recent trends, which have been relatively stable.

With no migration, there will be a fall in the size of St Helena’s population, because the number of deaths each year is likely to continue to be more than the number of births. The low and high migration models, however, both result in an increase in population size. Both the no migration and low migration scenarios result in a reduction in the working age population, and under all three scenarios the old age dependency ratio – the ratio of those aged 65 and over compared to those of working age – increases.

Under the no migration assumption, the total population falls by around 220 people by 2026, with a decrease of over 340 in the labour force and an increase of almost 150 in the number age 65 and over. The median age increases to 49, and the old age dependency ratio increases to 0.41 (only Japan currently has an old age dependency ratio higher than 0.41).

Under migration model 1 (low), the number of children age 15 or younger increases by almost 100 by 2026, the number in the labour force decreases by over 70, and the number of persons aged 65 and over increases by almost 190. The median age increase very slightly to 47, but the old age dependency ratio still increases substantially, to 0.39.

Under migration model 2 (high), by 2026 the number of children aged 15 and younger increases by 240, the number in the labour force increases by more than 480, and the number aged 65 and over increases by almost 300. The median age drops slightly to 45, and the old age dependency ratio still rises significantly, but at a slower pace.

Chart 1. Projected age distribution of St Helena’s population under three migration scenarios

Methodology

Population projections are based on assumptions about future patterns of fertility, mortality and migration. Key inputs are the age-specific fertility rates of women, the sex ratio at birth (i.e. the likelihood of a boy or girl), age-specific death rates of both men and women, and age-specific rates of emigration and immigration of men and women.

Estimates of age-specific fertility rates have been based on the ‘Average’ pattern published by the United Nations, adjusted for an estimated St Helena total fertility rate of 1.9 births per woman. The total fertility rate is the average number of children expected to be born to a woman over her lifetime assuming she lives throughout her reproductive years, and has been calculated using counts of local births, broken down by the age of the mother and the year of birth, and then combined with UK fertility rates.

The sex ratio at birth is assumed to be 105 male births per 100 female births, consistent with international averages.

Age-specific mortality rates are based on the patterns in the United Nations General Life Table, adjusted for life expectancy rates (at birth) on St Helena of 73 years for men and 79 years for women. Additionally, it has been assumed that life expectancy will increase by one year for every ten years of the population projection (in other words, if life expectancy is 73 in 2017 it will be 74 in 2027), consistent with the UN working model of life expectancy improvement.

While fertility and mortality rates are relatively stable, the third parameter – migration – is both highly volatile and very influential. Three variants have been used. The first is a no migration model, which assumes that there is no inward or outward migration (this is clearly unrealistic, but it provides a baseline). The second is a low immigration model, using the migration patterns between April 2014 and March 2015 which results in net immigration to St Helena of around 60 people per year. The third is a higher immigration model, assuming average migration patterns from 2010-16, resulting in net immigration of around 130 persons per year. In both the low and high migration models, temporary airport construction workers have been assumed to depart in 2017.

Table 2 summarises the migration assumptions in the two migration models (for full details, please refer to the data file). It should be noted that changes to the age and sex distribution of these models would yield different results. For example, migration model 2 (high) assumes the largest immigration in the 30-34 age group. Adjusting this to an older age group would result in an increase in the median age, and would likely impact the old age dependency ratio. Population projections using different assumptions about migration can be produced – please contact the Statistics Office.

The detailed calculations were completed the help of the Spectrum software package (version 5.41, DemProj module, see http://www.avenirhealth.org/software-spectrummodels.php#demproj). Many thanks are extended to Paula McLeod and Brendan Wahler, former Statistical Commissioner and staff member of the Statistics Office respectively, for preparing these projections.

Some Terms Explained

Old age dependency ratio: the ratio of the number of people aged 65 and over compared to the number of people aged between 15 and 64 (i.e. the approximate size of the labour force).

Median age: the age that divides the population into two equal groups. Half the population is younger than the median age, and half is older.

Sex ratio at birth: the number of male births per female births.

Age specific fertility rate: the number of live births per 1,000 women in a specific age group.

Total fertility rate: the number of children that would be born to a woman if she were to live to the end of her childbearing years.

Age specific mortality rate: the number of deaths per 1,000 population in a specific age group.

Life expectancy at birth: how long, on average, a new born can be expected to live, if current death rates prevail throughout their lifetime.

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