Documentation of the BEFINN and BEFREG Models
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Notater Documents 2014/25 • Kjersti Norgård Aase, Marianne Tønnessen and Astri Syse The Population Projections Documentation of the BEFINN and BEFREG models Documents 25/2014 Kjersti Norgård Aase, Marianne Tønnessen and Astri Syse The Population Projections Documentation of the BEFINN and BEFREG models Statistisk sentralbyrå • Statistics Norway Oslo–Kongsvinger Documents In this series, documentation, method descriptions, model descriptions and standards are published. © Statistics Norway Symbols in tables Symbol When using material from this publication, Statistics Category not applicable . Norway shall be quoted as the source. Data not available .. Published Data not yet available … Not for publication : Nil - ISBN 978-82-537-8952-1 (electronic) Less than 0.5 of unit employed 0 ISSN 1891-5906 Less than 0.05 of unit employed 0.0 Subject: Population Provisional or preliminary figure * Break in the homogeneity of a vertical series — Print: Statistics Norway Break in the homogeneity of a horizontal series | Decimal punctuation mark . Documents 25/2014 The Population Projections Preface This documentation report provides an overview of how projections for the Norwegian population are produced using the BEFINN and BEFREG models. The models were restructured in 2013–2014. The contents of this report therefore refer to how the projections published in June 2014 were made. More information about the population projections is available at www.ssb.no/folkfram. Statistics Norway, 20 May 2014 Hans Henrik Scheel Statistics Norway 3 The Population Projections Documents 25/2014 Abstract This report documents how Statistics Norway (SSB) produces population projections using the BEFINN and BEFREG models. In BEFINN, the population is projected by age and sex at the national level up to and including the year 2100. Immigrants from three country groups of origin, Norwegian-born children with immigrant parents and the remaining general population are projected as separate groups. In BEFREG, the population is projected by age and sex in 108 projection regions up to and including the year 2040. The population is thereafter distributed to counties, municipalities and city districts in Oslo. We use the cohort component method when projecting the population. This method requires two types of input: Updated figures for the population by sex and one-year age groups Assumptions about the future development of the demographic components fertility life expectancy domestic migration immigration Most of the assumptions that are used in the cohort component method are stated as rates, probabilities or proportions by sex and one-year age groups. The results of a population projection depend to a great extent on which assumptions are used about the components. The assumptions concerning future fertility, life expectancy, domestic migration and immigration are therefore produced in different alternatives: M – medium alternative H – high alternative L – low alternative K – constant alternative 0 – zero alternative Altogether, SSB projects the population in 15 combinations of these M, L, H, K and 0 alternatives. Each alternative is described using four letters in the following order: fertility, life expectancy, domestic migration and immigration. The term 'main alternative' is used to designate the MMMM alternative, which indicates that the medium level has been used for all components. 4 Statistics Norway Documents 25/2014 The Population Projections Contents Preface .................................................................................................................................. 3 Abstract ................................................................................................................................. 4 1. Introduction ............................................................................................................. 6 1.1. What are population projections? .............................................................................. 6 1.2. The process .............................................................................................................. 6 1.3. Publication ................................................................................................................. 7 1.4. Users ......................................................................................................................... 7 1.5. History ....................................................................................................................... 8 2. The projection models BEFINN and BEFREG ...................................................... 9 2.1. The cohort component method ................................................................................. 9 2.1.1 The method ............................................................................................................... 9 2.1.2. More about the assumptions ................................................................................... 10 2.1.3. Several events during the course of one year ......................................................... 10 2.1.4. Age at the end of the year ....................................................................................... 11 2.2. The BEFINN model ................................................................................................. 11 2.2.1. Results .................................................................................................................... 11 2.3. The BEFREG model................................................................................................ 12 2.3.1. Breakdown to the municipal level ............................................................................ 13 2.4. Calibration and rounding off .................................................................................... 14 2.4.1. Rounding off ............................................................................................................ 14 2.5. Alternative projections ............................................................................................. 14 3. Assumptions about fertility .................................................................................. 16 3.1. Data ......................................................................................................................... 16 3.2. Fertility for the country as a whole ........................................................................... 16 3.2.1. Fertility among immigrants ...................................................................................... 17 3.2.2. Fertility among the remaining population ................................................................. 17 3.2.3. Fertility assumptions................................................................................................ 17 3.3. Fertility at the regional level ..................................................................................... 18 3.3.1. Regional differences in fertility ................................................................................ 18 3.3.2. Fertility assumptions................................................................................................ 18 3.3.3. Breakdown of the figures to municipalities .............................................................. 18 4. Assumptions about mortality ............................................................................... 21 4.1. How do we project mortality? .................................................................................. 21 4.1.1. Data ......................................................................................................................... 21 4.1.2. Mortality rates .......................................................................................................... 21 4.1.3. The models ............................................................................................................. 22 4.1.3. Discretionary assessments ..................................................................................... 23 4.2. Life expectancy at birth and remaining life expectancy ........................................... 23 4.3. Mortality assumptions in BEFINN and BEFREG ..................................................... 24 5. Assumptions about immigration and emigration ............................................... 25 5.1. Immigration ............................................................................................................. 25 5.1.1. The model ............................................................................................................... 26 5.1.2. Data ......................................................................................................................... 27 5.1.3. Forecasts for the variables ...................................................................................... 28 5.1.4. Projected immigration .............................................................................................. 29 5.1.5. Distribution by age, sex etc. .................................................................................... 29 5.2. Emigration ............................................................................................................... 29 5.3. Net migration ........................................................................................................... 30 5.4. The number of persons with immigrant backgrounds .............................................. 30 6. Assumptions