In the theory of finance, a market for any asset or commodity is said to be efficient if items of identical quality and other attributes (such as risk, in the case of stocks) are sold at the same actual average price. a geneva-based oil industry analyst wants to test the hypothesis that the spot market for crude oil is efficient. the analyst chooses the rotterdam oil market, and he selects arabian light as the type of oil to be studied. (differences in location may cause price differences because of transportation costs, and differences in type of , in the quality of affect the price. therefore, both the type and the location must be fixed.) the analyst also notes that during the month of february 2008, the "official" price of a barrel of crude oil did not change. a sample of eight observations from each of four sources of the spot price of a barrel of oil during february is collected. data, u. s. dollars per barrel, are as follows: