@unpublished{publication-6291,
	author={Widmer, Philippe K and Zweifel, Peter and Farsi, Mehdi},
	institution={University of Zurich},
	issn={1664-7041 (P) 1664-705X (E)},
	number={No. 52},
	pages=19,
	series={Working paper series / Department of Economics},
	title={Accounting for heterogeneity in the measurement of hospital performance},
	year=2011,
}