Boyle, GlennGuthrie, Graeme2015-02-112022-07-062015-02-112022-07-061/07/20022002https://ir.wgtn.ac.nz/handle/123456789/18991We review the ability of the ex post internal rate of return (IRR) to detect monopoly profits. When market values are used as entry and exit values the ex post IRR simply reveals whether the firm did better or worse than the market expected at the entry date. It says nothing about monopoly profits. When replacement costs are used as entry and exit values the ex post IRR can in principle reveal something about monopoly profits. However since the ex post IRR is a noisy measure of ex ante monopoly profits it will be very difficult to reject the hypothesis given the sample periods typically available. The benchmarks typically used are market-determined and therefore only comparable to IRRs calculated using market values - a situation when the ex post IRR reveals nothing about monopoly profits anyway. Furthermore there is ample empirical and theoretical evidence that these benchmarks do not even represent fair rates of return.pdfen-NZPermission to publish research outputs of the New Zealand Institute for the Study of Competition and Regulation has been granted to the Victoria University of Wellington Library. Refer to the permission letter in record: https://ir.wgtn.ac.nz/handle/123456789/18870rates of returnmonopoly profitsText