Most applications of shift-share analysis to regional employment change have used a study period of several years and have examined conditions only at the beginning and end years. This comparative static approach does not take into account the continuous changes in both industrial mix and size of total employment of the region over the study period. Calculating the national growth effect. the industrial mix effect, and the competitive effect on an annual basis and then summing the results over the study period provides a more accurate allocation of job changes among the three shift-share effects. This approach, which we term dynamic shift-share analysis, also allows unusual years and years of economic transition to he identified. We illustrate the use of dynamic shift-share by presenting results of an analysis of New England employment growth from 1939 to 1984, using U.S. Bureau of Labor Statistics data. The use of the dynamic form of shift-share is important when the study period is characterized by either large changes in regional industrial mix or major differences between regional and national growth rates.HIFT-SHARE ANALYSIS is a relatively simple technique for an-S alyzing employment growth in a region over a specific time period.Fothergill and Gudgin (1979, p. 309) note that "shift-share fits the expectation that, when a technique is simple and apparently useful, it will be both widely used and heavily criticized." One set of criticisms arises from the temporal nature of the questions to which the technique is applied.' Most studies that use shift-share analysis have examined employment change over an interval of several years, and in so doing, considered conditions only at the beginning and end years of the time interval. This comparative static approach creates problems that we argue are eliminated by calculating the shift-share effects on an annual basis. We call this approach dynamic shiftshare analysis. We suggest that data availability and computational burdens, which at one time may have impeded the use of dynamic shift-share analysis, no longer form barriers to its application of an analysis of regional employment growth. We demonstrate the use of the dynamic shift-share approach with a brief case study of employment change in New England. Problems Associated with Comparative Static ApproachShift-share analysis decomposes employment growth (or decline) in a region over a given time period into three components: (1) a national growth Richard A . Bar8 is an assistant professor of geography at Dartmouth College. Prentice L. Knight III is Program Manager for the Industrial Development Research Council in Norcross, Georgia.

The relationship between immigration to and labor movements within the United States is examined using a model that links migration, occupations, production and institutional relations in the economy, and economic restructuring. The authors conclude that "native blue-collar workers have been spatially displaced by recent immigration and that the process of capital accumulation, as manifested in economic restructuring, is the driving force behind the mobility system, affecting both immigration patterns and the destination choices of white-collar workers. As a result, we suggest that previous estimates of immigrant impacts on local labor markets may be underestimated."

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The clustering of urban manufacturers occurs for a number of reasons; this paper focuses on the importance of production technology in understanding the degrcc of industrial clustering. The present analysis uses a sample of Cincinnati manufacturing plants to test scveral hypothescs that address the relationships between industrial clustering and industrial production technology. Most of the tests use second-order methods to distinguish between the spatial distributions of specificd classes of industry. The analysis reveals that the functional disintegration of productive activity leads to increased degrees of industrial clustering in urban space. Furthermore, the dispersal that occurs through plant relocation is not a simple centrifugal process but a subtle modification of the clustered pattern of urban industry.

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