previous | contents | next

Projected Population of Scotland (2012-based)

Annex A: Fertility assumptions

Fertility assumptions are agreed in two stages. The long term assumption is decided as part of the consultation process between the UK countries and the Office for National Statistics. Then there is detailed assumption setting to produce the age-specific fertility rates for each year of the projection period that are consistent with the long-term assumption.

The fertility assumptions for the long-term average completed family size have been increased by 0.05 for each UK constituent country since the 2010-based population projections. This increase is based on the observation that the falling completed family size of women has slowed and period fertility rate levels have stabilized in recent years. The Scottish long-term assumption is still lower than the assumptions for other UK countries. The assumptions for Scotland and other constituent countries of the UK are given in Table A1.

Table A1: Assumptions of long-term average completed family size, 2010 and 2012-based projections

2012-based 2010-based
England 1.90 1.85
Wales 1.90 1.85
Scotland 1.75 1.70
Northern Ireland 2.00 1.95
United Kingdom 1.89 1.84

The trends in age specific fertility for Scotland are shown in Figure A1. Until 2002, there is a general pattern of falling fertility at younger ages coupled with rises in fertility at older ages.

Recent data have shown increases in fertility rates until 2008, and then a slight decrease in the last two years. The biggest increases in fertility rates are for women in their thirties. Fertility rates increased for women in their twenties from 2001 to 2008, but they have fallen in recent years. Fertility rates for women over 40 is the only age group to see a continued rise to 2011 although there has been a stabilization in 2011 and 2012.

Figure A1: Scotland age specific fertility, 1983-2012

Figure A1: Scotland age specific fertility, 1983-2012

Fertility assumptions are formulated in terms of the average number of children that women born in particular years will have. This cohort measure of fertility is more stable than the analogous calendar year or period measure (the total fertility rate). This is because it is affected only by change in the total number of children women have and not by the timing of births within their lives. Period rates may rise or fall if births are brought forward or delayed for any reason.

The assumptions about completed family size are based on family building patterns to date and other relevant data. For the UK as a whole, the steady decline in achieved family size at each age, a clear pattern for the 1945 to 1975 cohorts, appears to be bottoming out among the most recently-born cohorts of women.

For Scotland, fertility rates are assumed to continue to increase for women in their 40s, remain stable for women in their 30s and fall slightly for women in their 20s.

The Total Fertility Rate (TFR) for Scotland is projected to increase until 2030 before reaching the long term level.

The high and low fertility variants assume long-term family sizes of 0.2 children per women higher or lower than the principal projection, that is, 1.95 and 1.55 children per women for Scotland.

previous | contents | next