Theoretically speaking, the curve is a diagonal (opportunity line
) drawn from the origin to the top right corner; ROC curve is usually located above the opportunity line
, the further from the opportunity line
the higher the accuracy of prediction; the area under ROC curve (Area Under Curve, AUC) can reflect the accurate degree of the diagnostic experiment, and the value of this index drops within 0.5-1, and the value 0.5 - 0.7 indicates lower accuracy of prediction; 0.7 - 0.9 indicates intermediate accuracy; and value above 0.9 indicates higher accuracy.
He embellished this basis with a foreign element which he called the "exchange opportunity line." According to Blau, this latter represents "A fair rate of exchange, based on accepted social norms of what is a fair return (in compliance) for expert advice" (p.
The reader should be forewarned that the conflicting paradigms overlaid one on top of the other in figure 3 will require discontinuities in discussion as Blau's attention shifts from Edgeworth's neoclassical model to the Durkheimian ideas embodied in the exchange opportunity line. Commencing with the latter, one might have expected Blau to offer the exchange opportunity line as the solution to the indeterminacy problem which had so offended Edgeworth.
It is as if Blau disaggregated some original set of indifference curves, culling from them the "price norm influences" he needed for the exchange opportunity line, which he then presented in his Figure 2 (p.
There is a peculiar way in which the exchange opportunity line serves both to facilitate Blau's shift of paradigm and at the same time conceal the nature of his undertaking.
Not only does it provide a summary of the nature and forces of retail competition but it also introduces the central and recurring themes of the book, strategic groups and the "shopping opportunity line
" (a form of price-quality continuum).
I soon discovered that the agencies' job opportunity lines are no better maintained than their information hot lines.
The job opportunity lines of three of the agencies I phoned, the Departments of Energy, Commerce, and Justice, were not in service.