=Efficiency achieved through contracting=
Despite these commonly held views, contracted service yields only moderate cost savings. In a study of 400 transit agencies spanning a 10 year period from 1992 to 2002, partially contracted service yielded a 7.8
% cost savings while contracting all service yielded only a 5.5 % savings.<ref name="Iseki 2004">Iseki, Hiroyuki (2004), “Does Contracting Matter? The Determinants of Contracting and Contracting’s Effects on Cost Efficiency in US Fixed-Route Bus Transit Service”, University of California, Los Angeles, unpublished dissertation.</ref> Research has also shown a strong self selection bias to be present among transit agencies. If an agency can achieve cost savings through contracting either a part or all of its service, it will do so. Other agencies efficiently delivering their own directly provided service are much less likely to contract service. Thus, transit agencies cannot necessarily look to other agencies for guidance on the choice of contracting.