Toward a Systematic, Argument-Based Approach to Defining Assumptions for Population Projections

Lutz, W. ORCID: https://orcid.org/0000-0001-7975-8145 (2009). Toward a Systematic, Argument-Based Approach to Defining Assumptions for Population Projections. IIASA Interim Report. IIASA, Laxenburg, Austria: IR-09-037

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Abstract

This paper proposes a new approach for defining the assumptions in population projections. It is based on a broad discussion and argumentation exercise which critically assesses the science basis of alternative arguments that relate to the forces which jointly shape the future trends in fertility, mortality and migration. It starts by discussing the results of a recent Eurostat survey among all EU national statistical offices in which there appears a clear consensus that the current practice of defining assumptions for population projections should be improved through stronger interactions with the scientific community. As an instrument for such interactions, the paper goes on to propose an interactive spreadsheet in which more than 100 arguments relating to the forces shaping future fertility, mortality and migration have been formulated. Invited experts then evaluate these arguments with respect to their validity and their potential impacts on the force under consideration. This interactive questionnaire has already been used to define the assumptions in the official UK population projections and with an international group of 17 mortality experts. With further fine tuning, this approach can be used to collect and synthesize the expertise of large numbers of experts for defining median assumptions and the associated ranges of uncertainty. It has the potential to become a standard tool for the future production of national and international population projections.

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