Understanding Recent Fertility Trends in the UK and Improving Methodologies for Fertility Forecasting

The last two decades have witnessed dramatic fluctuations in fertility levels, which were not predicted by demographers or government statisticians: Fertility significantly increased in the first decade of the 21st century, whereas it has declined thereafter. These fluctuations have significant implications for planning and policy making, at both national and local levels. For example, the fertility increase between 2001 and 2012 led to more than 60 thousand additional births in the UK annually. The causes of the recent fertility dynamics are unclear. Some researchers attribute the recent fluctuations in fertility levels to changes in fertility timing - i.e. the postponement or acceleration of childbearing. Others emphasise the importance of changes in population composition or changes in childbearing behaviour in response to past policy changes and the post-2008 economic recession. Birth registration data used by government statisticians at the Office for National Statistics (ONS), National Records of Scotland (NRS) and Northern Ireland Statistical Research Agency (NISRA) inform us about the total number of births and aggregated fertility measures; however, they do not provide information about childbearing trends by parity (birth order), which is critical to understanding and predicting fertility trends. High-quality large-scale longitudinal data provide the opportunity to conduct a detailed analysis of parity-specific fertility; for example, to determine whether fertility has recently declined because of the (further) postponement of childbearing and increased childlessness among women or because of declining family size among mothers (e.g. fewer third births).

Childbearing is naturally a sequential process; decisions on having an additional child are likely to be evaluated on the basis of experience with previous children. Detailed analysis of fertility by parity will thus significantly enhance our ability to forecast future fertility. In this project we will harmonise census-linked administrative data from the ONS Longitudinal Study, Scottish Longitudinal Study, and Northern Ireland Longitudinal Study, together with survey data from the Understanding Society study.

The project is thus novel in that it uses data from the all four UK constituent countries; focuses on the analysis of childbearing trends by birth order, and brings together experts in demography and statistical forecasting to develop better methods for fertility forecasting.

First, we will calculate annual parity-specific fertility rates by UK country to determine how much changes in fertility levels are attributable to the changes in first, second, third or fourth births. We will then adjust fertility rates for characteristics of that population (e.g. place of birth, educational level) to determine how much a change in fertility levels in the UK over time is attributable to changes in population composition, and how much to changes in childbearing behaviour, possibly as a result of changing policies and economic environment. Finally, we will use information on parity-specific fertility to forecast future fertility levels in the UK using Bayesian methodology.

The project will bring together researchers from the Universities of St Andrews and Southampton, as well as government statisticians from ONS, NRS, and NISRA, to work on an important policy-relevant topic. The project will greatly improve our understanding of the factors associated with changing fertility dynamics in the UK and will show how existing large-scale longitudinal datasets can be used for cross-country analysis of fertility by birth order. It will also significantly improve the methodology used for fertility forecasts for the UK and its constituent countries. A better understanding of the present childbearing trends and forecast of the future developments will be critical to inform the planning of demand for various public services (e.g., nurseries, school places and housing).

Who will benefit from this research?
The project will have both academic and societal impact. The major group of academic beneficiaries will be researchers from the fields of demography, sociology, political science, economics, human geography, social statistics, social policy, and others interested in measuring, explaining and forecasting human fertility. The major group of non-academic beneficiaries will be family, population and social policy analysts and government statisticians working at the statistical offices of the UK's constituent countries: the Office for National Statistics (ONS), the National Records of Scotland (NRS) and the Northern Ireland Statistics and Research Agency (NISRA); and at local authorities. ONS and NRS are the project partners and NISRA and two local authorities are the key stakeholders (the Greater London Authority and Hampshire County Council). We also expect that people involved in decision-making in the areas of family, population and social policies will be interested in the results of the study. Finally, the results of the project will be of interest to the general public in the UK.

How they will benefit?
The project will provide rich and reliable information on childbearing dynamics in the UK; it will investigate the causes of changing fertility levels and will develop improved methodologies for fertility forecasting. The results of the project are, first, of interest of academic researchers as they will deepen our understanding of the reasons for significant short-term fluctuations in fertility levels in advanced economies and will provide better tools to analyse current childbearing trends and project future developments. Second, the proposed methodology for fertility analysis and forecasting will help the UK's statistical agencies and local authorities produce more accurate population projections at national, country and local levels. Improved projections are critical to estimate future need for hospital delivery, school places and demand for housing at national and sub-national levels. Third, the results of the project will be important for people involved in decision-making in the areas of family, population and social policies to understand whether and how family policies introduced in the UK in the late 1990s have shaped childbearing trends and patterns in the UK. Finally, it is equally important to inform the general public on the short- and long-term fertility trends in the UK and their impact on wider population and social trends (e.g. population ageing).