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This paper examines the widespread practice where data envelopment analysis (DEA) efficiency estimates are regressed on some environmental variables in a second-stage analysis. In the literature, only two statistical models have been proposed in which second-stage regressions are well-defined and meaningful. In the model considered by Simar and Wilson(More)
Speciation involves the formation of reproductive isolating mechanisms such as a difference in pollinators, incompatibility between pollen tubes and stylar tissue, hybrid seed abortion, or poor growth of hybrid seedlings. We studied reproductive isolating mechanisms in naturally sympatric populations of Penstemon spectabilis Thurber and Penstemon(More)
This paper discusses various statistics for testing hypotheses regarding returns to scale in the context of non-para-metric models of technical efficiency. In addition, the paper presents bootstrap estimation procedures which yield appropriate critical values for the test statistics. Evidence on the true sizes and power of the various proposed tests is(More)
Research concerned with symbiotic nitrogen-fixation is conveniently divided into three periods in which the type of problem that has attracted major emphasis has varied. The pioneer labors of Liebig, Lawes and Gilbert, Boussingault, Ville, Atwater, and of others initiated the first period which was concerned primarily with the specific question : Are green(More)