We propose a model of contracting for natural monopolies in which yard
stick evaluation of performance can be optimal. Where principals have
partially unobservable objective functions and agents are risk averse
an externality is generated which can be observed in patterns of spati
al dependence, Imposing standard contracting rules on principals can e
liminate the externality and spatial dependence. We test this predicti
on using spatial econometrics on UK data covering a regime shift from
independent contracting to compulsory competitive tendering rules. (C)
1997 Elsevier Science S.A.