1. Strategy Unit, Harvard Business School, Boston, Massachusetts 02163;
2. Robert H. Smith School of Business, University of Maryland, College Park, Maryland 20742;
3. Leeds School of Business, University of Colorado, Boulder, Boulder, Colorado 80309;
4. Strategy and Business Policy, École des Hautes Études Commerciales de Paris, 78351 Jouy-en-Josas Cedex, France