What is the optimal fertility rate?

By Erich Striessnig, IIASA World Population Program

Credit: Héctor Gómez Herrero via Flickr (Creative Commons License)

Is replacement level fertility really the best for society? Maybe not, say IIASA researchers. Photo Credit: Héctor Gómez Herrero via Flickr (Creative Commons License)

When asked what a desirable fertility level for populations might be, most politicians, journalists, and even social scientists would say it is around two children per woman, as this would – on the long run – prevent a population from either exploding or dying out. Other reasons for championing replacement level fertility include maintaining the size of the labor force and stabilizing the dependency ratio. But what is the evidence for this rule of thumb?

My colleague Wolfgang Lutz and I aimed to answer this question in a new study published in the journal Demographic Research. We found, not surprisingly, that the optimal fertility level strongly depends on what you mean by optimal.

The criteria for optimal fertility have often been motivated by nationalistic desires for larger and thus more powerful nations. Today our concerns run more towards the dangers of overpopulation for the environment, the climate, and the limited resources on Earth, dampening the enthusiasm for high fertility rates. But as fertility rates fall in many countries around the world, there is a growing concern about aging populations and an increasing number of elderly depending on an ever smaller number of people actively participating in the labor force.

While all of these fears relate to the same problem – an unbalanced population age-structure – the resulting assessments of what level of fertility would be desirable completely ignore the heterogeneity of the population with regard to important demographic characteristics, especially the population’s education structure.

In our study, we wanted to account for the fact that more education not only has higher economic costs, including later entry to the labor market and higher life expectancy, which can hardly been seen as a negative effect. But education also leads to higher productivity, less unemployment, and a healthier workforce that would on average retire later. To include these factors in our assessment, we ran thousands of simulations using varying constant rates of fertility.

What we found is that when we factor in education, the level of fertility that on the long run would lead to the lowest level of dependency is well below the supposedly magical level of two children per woman.

We also tried to link the effects of different fertility rates to the resulting environmental burden by factoring in expected carbon emissions. Not surprisingly, higher rates of fertility lead to faster population growth and more emissions. That suggests that an environmentally aware society should aim for even lower fertility levels.

While our research is not intended to prescribe fertility levels for individuals and countries, the conclusions drawn from this thought experiment suggest that the widespread popular notions that current fertility levels–for example in France or the US are just right because they are around replacement level, whereas they are too low in countries like Germany or Austria–may be wrong. According to our new study, the opposite is true.

Striessnig, E, Lutz W. (2014) How does education change the relationship between fertility and age-dependency under environmental constraints? A long-term simulation exercise Demographic Research, 30(16):465-492 http://www.demographic-research.org/volumes/vol30/16/

Note: This article gives the views of the author, and not the position of the Nexus blog, nor of the International Institute for Applied Systems Analysis.

How can Europe cope with multiple disaster risks?

Interview with IIASA risk expert Nadejda Komendantova

In a new study, IIASA Risk, Policy, and Vulnerability Program researcher Nadejda Komendantova and colleagues from Germany and Switzerland examined how natural hazards and risks assessments can be incorporated into decision-making processes in Europe on mitigation of multiple risks. 

A cyclist rides along the flooded Danube River in Braila, Romania, in 2010. Credit: cod_gabriel on Flickr

A cyclist rides along the flooded Danube River in Braila, Romania, in 2010. Credit: cod_gabriel on Flickr

Why did you decide to conduct this study?
European decision makers currently have a number of methods that they can use to assess natural hazards and risks and apply to the decision-making process. These methods include risk and hazard assessments, probabilistic scenarios, and socio-economic and engineering models.  The variety of tools is enormous and volume of knowledge and data is growing. However, the process of communication  between science and practice leaves a lot of open questions for research.

Researchers have developed a few tools to provide multiple risk assessment of a given territory. But even though these models have been tested by operational and practicing stakeholders, there is limited information about how useful the models are for civil protection stakeholders to use in practice.  In order to communicate results from science to practice and make it possible for decision-makers to use such tools, it helps to involve decision-makers in the development process. Participatory modeling, which is an important part of risk governance, allows us to not only to take into consideration the facts, but also values and judgments that decision-makers bring to their actions.

What questions did you aim to answer in your study?
The decision-making process becomes even more complex when we talk about situations with multiple risks – multi-risks – which involve interactions between several risks. How will decision-maker will prioritize their actions on risk mitigation or on resources allocation when facing not single but multiple risks? We also wanted to find out if the tools developed by science such as decision support models could be suitable for these tasks. Another question is if there are differences in perceptions of the usability of decision-support tools between different stakeholders, such as academia (based on more theoretical considerations) and civil protection (based on practice).

What are the multiple risks or hazards that face Europe?
Across Europe, people suffer losses not just from single hazards, but also from multiple events in combination. The most important hazards for Europe are earthquakes, landslides, volcanic eruptions, tsunamis, wildfires, winter storms, and floods along both rivers and coastlines.

What methods did you use to conduct your study?
To answer our research questions we collected feedback from civil protection stakeholders on existing risk and hazard assessment tools as well as on the generic multi-risk framework to understand interrelations between different risks, such as conjoint and cascade effects. The new study was based on a method developed by Arnaud Mignan at ETH Zürich, with a decision-support tool developed by Bijan Khazai at the Karlsruhe Institute of Technology. Through a participatory approach, the decision-support tool allowed  stakeholders to assign relative importance to the losses for different sectors for each of the scenarios likely to occur in the region.

We collected data through questionnaires on existing risk assessment tools in Europe and their implementation. Then, using the new framework, we conducted focus group discussions in Bonn and Lisbon, and decision-making experiments applying the developed tools. Afterwards we had a chance to collect feedback from stakeholders.

What did you find?
The study showed that general standards for multi-risk assessment are still missing—there are different terminologies and different methodologies related to data collection, monitoring, and output. According to stakeholders from practice, this variety of data, assessment methods, tools and terminology might be a barrier for implementation of the multi-risk approach.

The study also found a sharp divide in understanding of the usability of the tools and areas for their application. Academic stakeholders saw the risk-assessment tools as being useful to understand loss and communication of multi-risk parameters. The stakeholders from practice instead saw  the tool as more useful for training and educational purposes as well as to raise awareness about possible multi-risk scenarios.

What should be done to help decision-makers make better decisions?
The study made it clear that we need to work on training and education, both for policymakers and the public. The models we have developed could be useful for educating stakeholders about the usefulness of a multi-risk approach, and to disseminate these results to the general public. It was recommended to use the tools during special training workshops organized for decision-makers on multi-risk mitigation to see possible consequences of a multi-hazard situation for their region. Participatory modeling, involving cooperation between scientists and decision-makers from practice, could not only improve communication processes between science and policy. In addition, decision-support models can become a part of dialogue to help to avoid judgment biases and systematic errors in decision-making and to help in complex decision-making process grounded on human rationality and judgment biases.

Nadejda Komendantova, Roger Mrzyglocki, Arnaud Mignan, Bijan Khazai, Friedemann Wenzel, Anthony Patt, Kevin Fleming. 2014. Multi-hazard and multi-risk decision support tools as a part of participatory risk governance: Feedback from civil protection stakeholder. International Journal of Disaster Risk Reduction. http://www.sciencedirect.com/science/article/pii/S221242091300068X

Note: This article gives the views of the interviewee, and not the position of the Nexus blog, nor of the International Institute for Applied Systems Analysis.