Acknowledgements

The authors are indebted to Bob Gibson of the Economic Analysis Division for the preparation of data and to Desmond Beckstead and Mark Brown of the same division for their many helpful comments and suggestions. We are also grateful for comments that we received on earlier versions of this paper from participants at the Annual Meetings of the Canadian Economics Association (May 2005), at the Industry Canada Economic Seminar Series (January 2006), and at the North American Regional Science Council Annual Meetings (November 2008).