This thesis synthesizes different perspectives on scale choices (spatial boundary setting, temporal boundary setting and the selection of the level of aggregation) in policy analysis. Scale choices influence the content of a study: the problems on the agenda, the options found and the impacts addressed. This also affects the process because scale choices are not politically neutral: they may advantage or disadvantage certain actors by putting their urgent problems, their preferred options on the agenda and may hide or stress the positive or negative impacts of options. In my opinion, it is important to pay sufficient attention to scale choices in the design of a policy analysis process because they have a large influence on the policy analysis process and its outcome.

Yet, little is known about the specific effects of the spatial boundary setting, the temporal boundary setting and the selection of the level of aggregation and how they are made in practice. In this research, the making of scale choices is studied using two empirical cases: the Long-Term Vision of the Scheldt Estuary and the Water Shortage Study of the Netherlands. Scale choices appear to be an important framing instrument that can be used by policy analysts. Only a relatively small group of people calls themselves policy analysts. However, a large group of people perform policy analysis processes without labelling themselves policy analysts: often governmental officials occupied with preparing policy documents. I hope that policy analysts in the broad meaning of the word consider this thesis useful in making decisions in the design of a policy analysis process, maybe even in a broader context than making scale choices. I hope that experienced policy analysts recognise the importance of the problems addressed in this thesis, and that it makes their relevant tacit knowledge explicit and accessible to others. Also, I hope that other readers of this thesis understand what a challenging endeavour policy analysis is: balancing on a thin line in the gap between politics and scientific research.

I would like to use this opportunity to thank many people who have been of vital importance during this research and writing process.

Wil Thissen and Pieter Bots, my professor and my daily supervisor: I thank you both for providing a unique combination of ultimate reflection and creativity to find solutions for problems. Thanks to all the people at the section of Policy Analysis of the Faculty of Technology, Policy and Management of the Delft University of Technology for the stimulating discussions on policy analysis research. Many thanks to Linda Carton, my roommate, for the years I spent at the University and for the many interesting and endless discussions we had on research and life in general. Warren Walker, indeed, at the start I thought I was going to write the bible on this subject; I hope you consider this a modest introduction! Thanks to my peers Maura Soekijad, Mirjam Huis in 't Veld, Heleen Weening, Mark de Bruijne, Ruben van Wendel de Joode, Leon Hermans, Alexander de Haan and Linda Carton for many interesting and inspiring Friday afternoon discussions on research.

I am very grateful to Menzo de Muinck-Keizer, my manager at the start of this study, for the opportunity to combine work and research that was provided by GeoDelft. Also, I would like to thank the director and managers who believed in the benefit of what I was doing at this ‘strange’ faculty from the beginning: Joost Wentink, Marco Hutteman, Gerben Beetstra, Peter van den Berg and Harm Aantjes. My enthusiastic direct colleague who tried to keep me out of the wind when I really had to write: Jurjen van Deen, you are a true mentor to me! And you were right: De kunst van het afronden van een proefschrift is niet om de puntjes op de i te zetten, maar om er een punt achter te zetten.

Also, thanks to all the new Deltares colleagues for the enthusiastic discussions in the Gamma Werkgroep, the Staat en Toekomst van de Delta, and the Waterplan verkenningen and my new department, Strategic Exploration and Innovation Management, and the colleagues in the Water Innovation program WINN, that inspired me again in this research. I really hope we can continue to learn from each other in the coming years. And thanks too, to my new managers Lucas Janssen and Hans Vissers who kept convincing me that it was important to finish the boekie soon. Thanks also to the many, many other colleagues who regularly kept asking how my research was going even though it took longer than planned.

Many people were involved in the cases. It would take too long to mention them all here individually, but I want to thank the interviewees listed in Appendix 2 and 3 for their enthusiastic contribution to the often long interviews. Special thanks to Harm Albert Zanting, Marieke de Groen, Fon ten Thij and Harold van Waveren for the many interesting discussions about the cases and policy analysis, in general. They showed me what being a policy analyst really comprises. A special word of thanks to the participants of the conference of the World Water week in Stockholm and the Conference on Building Bridges in Water Management in Kalmar, both in August 2003. I received so many enthusiastic and stimulating reactions to the survey that I held and had many interesting discussions on the subject. This was a final confirmation for me that the research that I was doing did indeed matter.

To all the friends of the Mijnbouwgroep, thanks for the social distraction during the weekends, the Christmas dinners and the ladies' dinners: I think it is really special to undertake these kinds of activities with such a large group of friends. I hope we can keep doing so even now that more and more little miners are giving acte de presence.

Berber and Saskia, my best friends, although the physical distance between us has been growing, I am convinced that our friendship can withstand the challenge. Berber, I was really pleased that you insisted on being my paranymph and coming all the way from Norway to do so. I thank you both for your support. I truly hope we can effectuate the agreement we made in the Efteling in 2001.

Thanks to my parents who are always encouraging me to get the most out of myself, for their everlasting interest in all the things I am doing, and for all the worrying about my busy life. Het kopke neemt nu wat meer rust, beloofd.

And last but not least: Thank you René, for your everlasting support and for being a true soul mate. Funny how words always seem to fall short when it comes to the most important person to thank...