What is “power”? Most people have an intuitive notion of what it means. But scientists have not yet formulated a statement of the concept of power that is rigorous enough to be of use in the systematic study of this important social phenomenon. Power is here defined in terms of a relation between people, and is expressed in simple symbolic notation. From this definition is developed a statement of power comparability, or the relative degree of power held by two or more persons. With these concepts it is possible for example, to rank members of the United States Senate according to their “power” over legislation on foreign policy and on tax and fiscal policy.

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The authors have developed a technique to estimate input functions from a population-based arterial blood curve in positron emission tomography (PET) studies with fluorine-18 fluorodeoxyglucose (FDG). A standardized pump injection was used in 34 subjects. A population-based blood curve was generated based on the first 10 subjects. In the remaining 24 subjects, an estimated input function (EIFa) was obtained by scaling the population-based curve with two arterial blood samples, one obtained at 10 minutes and the other at 45. Time integrals for EIFa and the real arterial input function (RIF) were in excellent agreement (r = .998, P < .0001). Cerebral metabolic rates for glucose calculated with EIFa and RIF and the autoradiographic method also correlated excellently (r = .992, P < .0001). Analogous correlations were achieved with arterialized venous samples as scaling factors. These results suggest that individually scaled, population-derived input functions may serve as an adequate alternative to continuous arterial blood sampling in quantitative FDG-PET imaging.

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I need hardly remind this audience that one of the characteristics of our field is the large number of old and quite elemental questions—elemental but by no means elementary—for which we have no compelling answers. I don't mean that we have no answers to these questions. On the contrary, we often have a rich variety of conflicting answers. But no answer compels acceptance in the same way as a proof of a theorem in mathematics, or a very nice fit between a hypothesis and a satisfactory set of data.Whether the obstacles that prevent us from achieving tight closure on solutions lie in ourselves—our approaches, methods, and theories—or are inherent in the problems is, paradoxically, one of these persistent and elemental questions for which we have a number of conflicting answers. For whatever it may be worth, my private hunch is that the main obstacles to closure are in the problems themselves—in their extraordinary complexity, the number and variety of variables, dimensions qualities, and relationships, and in the impediments to observation and data-gathering.However that may be, a question of this sort often lies dormant for decades or even centuries, not because it has been solved but because it seems irrelevant. For even when no satisfactory theoretical answer exists to a very fundamental question, historical circumstances may allow it to be ignored for long periods of time. Even specialists may refuse to take a question seriously that history seems to have shoved into the attic. What seem like fundamental controversies in one age are very likely to be boring historical curiosities in the next. And conversely it is my impression that a great many of the elemental political questions regarded as settled in one age have a way of surfacing later on.

afforded the opportunity to review ourselves. The years pass, we labour in new domains, rarely do we reflect critically on our earlier workthough our reputations and the body of our subsequent work may rest on it. In this new intermittent serieswe dub it 'Author/Author'-Government and Opposition proposes to invite distinguished political scientists and theorists who have written books of enduring significance to choose one of their earlier works and reflect selfcritically and retrospectively on it. What are the circumstances of its composition? How did it influence subsequent work? Was its critical reception just? Have its basic argumc..s held up over time? How might they be revised in the light of later developments in political science and the political world? Each instalment of 'Author/Author' will respond to these kinds of questions. Our inaugural article is from Robert Dahl, one of the great political scientists of the postwar era, a former President of the American Political Science Association, and the winner of many awards, including, for his most recent book Democracy and Its Critics, the Woodrow Wilson Award of the American Political Science Association and the Spitz Award of the Conference for the Study of Political Thought. For us, Dahl has chosen to review his Preface to Democratic Theory.