The paper is prompted by certain apparent deficiences both in the discussion of the regression model in instructional sources for geographers and in the actual empirical application of the model by geographical writers. In the first part of the paper the assumptions of the two regression models, the 'fixed X' and the 'random X', are outlined in detail, and the relative importance of each of the assumptions for the variety of purposes for which regression analysis may be employed is indicated. Where any of the critical assumptions of the model are seriously violated, variations on the basic model must be used and these are reviewed in the second half of the paper. THE rapid increase in the employment of mathematical models in planning has led R. J. Colenutt to discuss 'some of the problems and errors encountered in building linear models for prediction'. 1 Colenutt rightly points out that the mathematical framework selected for such models 'places severe demands on the model builder because it is associated with a highly restrictive set of assumptions. .. and it is therefore imperative that, if simple linear models are to be used in planning, their limitations should be clearly understood'. 2 These models have also been widely used in geography, for descriptive and inferential purposes as well as for prediction, and there is abundant evidence that, like their colleagues in planning, many geographers, when employing these models, have not ensured that their data satisfied the appropriate assumptions. Thus many researchers appear to have employed linear models either without verifying a sufficient number of assumptions or else after performing tests which are irrelevant because they relate to one or more assumptions not required by the model. Furthermore, many writers, reporting geographical research, have completely omitted to indicate whether any of the assumptions have been satisfied. This last group is ambiguous, and it is clearly not possible, unless the values of the variables are published, to judge whether the correct set of assumptions has been tested or, indeed, to ascertain whether any such testing has been performed at all. This problem partially arises from certain shortcomings in material which has been published with the specific objective, at least inter alia, of instructing geographers on the use of quantitative techniques. All of these sources make either incomplete or inaccurate specifications of the assumptions underlying the application of linear models, although it is encouraging to note that there has been a considerable improvement in the quality of this literature in recent years. Thus, there were four books and two articles published in the early and mid-1960s which may be classified as belonging to this body of literature, 3 yet, in five of these six sources, only one of the assumptions of the model is mentioned and, even

ABSTRACT. The segregation of Catholics and Protestants varies spatially and temporally in Belfast, Northern Ireland. Using small‐area statistics from the censuses of 1971, 1981, and 1991, taken during the recent “Troubles,” a strongly rising level of ethnic segregation is noted for the 1970s, followed by a more gentle rise in the 1980s. Segregation is shown to vary among subunits of the urban area. The basic cause of this segregation is ethnic violence, and the spatial variation in segregation can be attributed to spatial variation in this violence.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. American Geographical Society is collaborating with JSTOR to digitize, preserve and extend access to Geographical Review. ABSTRACT. The segregation of Catholics and Protestants varies spatially and temporally inBelfast, Northern Ireland. Using small-area statistics from the censuses of 1971, 1981, and 1991, taken during the recent "Troubles," a strongly rising level of ethnic segregation is noted for the 1970s, followed by a more gentle rise in the 198os. Segregation is shown to vary among subunits of the urban area. The basic cause of this segregation is ethnic violence, and the spatial variation in segregation can be attributed to spatial variation in this violence.Since 1968 Northern Ireland has experienced a period of violent conflict unprecedented in length and intensity in this part of the United Kingdom. The current "ceasefires" are only the latest twist in an ever-changing scenario. Intercommunal strife, paramilitary activity, and security-force response have produced great trauma: More than 3,000 thousand people have been killed (from a population of around 1.5 million), thousands more have been injured, and immense destruction has been wrought on livelihoods and property.These "Troubles"-to adopt the local euphemism-are but the most recent out- pourings from an intermittently active vent of violence that was added to the already turbulent landscape of Irish political conflict by the arrival of immigrant British settlers in the sixteenth and seventeenth centuries. This colonization occurred primar-ily in the northern part of the island, and one of its outcomes is that, four hundred years later, the people here are still substantially divided into two communities who perceive their history in terms of the settler-native division established so long ago (Buchanan 1982). One of these groups forms what is now the Catholic minority in Northern Ireland, and it sees itself as descended from the native Irish population. In contrast, the Protestant majority views itself as descended from English and Scots immigrants. Conventional media and everyday labels describe the protagonists in Northern Ireland's contemporary political violence as partisans in an essentially religious conflict. However, the core issues are ethnonational identity and allegiance (O'Duffy 1995). Most Catholics espouse an all-Ireland nationalist ideology that favors political * We adapted the 1991 data from the Northern Ireland Census 1991 small-area statistics by permission of the Controller of Her Majesty's Stationery Office and the Department of Finance and Personnel. Other census material ? Crown Copyright 1994. We acknowledge the financial assistance that enabled us to purchase the data sets used in this s...

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