Acknowledgements
The author is grateful to a number of people who helped with this paper. Refreshing discussions took place with Jasper de Bruin, Wouter Vos and Ab Waasdorp. Wouter Vos is also thanked for reading the first version of this paper. Special thanks go out to Jean Paul Bakx, Elles Besselsen, Wim De Clercq, Joris Lanzing, Heleen van Londen, Linda Therkorn and Henk van der Velde for their useful additions to the dataset. Everhard Bulten and Diederick Habermehl are thanked for making the publication of this paper possible.
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Jeroen van Zoolingen
Gemeente Den Haag
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Review data:
Submission 15/12/2010
Revision 16/1/2011
2nd submission 25/3/2011