Comparison of individual and paired learning for the measurement of retention

Thesis (Ed.M.)--Boston UniversityThe purpose of this study was to measure and compare retention between children working alone and with a partner using S.R.A. (Scientific Research Associates) reading materials. The S.R.A. laboratory is a series of graded reading experiences intended to be used by individual children working alone and at their own rate of speed. Its general purpose is to improve many reading skills but in this study the retention factor will be the only concern

Heteroduplex analysis of tra delta f' plasmids and the mechanism of their formation

Four tra delta FargG+ plasmids, derived from matings between Hfr AB312 and a recA recipient, have been shown to have deletions of at least 50% of the F genome, including the region in which the tra genes map. The mutant plasmids do contain the F genes required for plasmid maintenance. Correlations can be made between, on the one hand, the F genes present on the tradelta F' plasmids and the F genes transferred early by an Hfr donor, and, on the other hand, the F genes deleted from the tradelta F' plasmids and the F genes transferred late by an Hfr donor. A biased representation of proximally and distally transferred chromosomal markers among the tradelta F' elements was also demonstrated. Taken Taken together, the asymmetrical representation of Hfr genes and the cis dominance of the Tra phenotype of these mutants can best be explained by the hypothesis that the tradelta F' plasmids are formed by repliconation of the transferred exogenote in a recA recipient

Concentration Levels in the U.S. Advertising and Marketing Services Industry: Myth vs. Reality

This paper analyzes changes in concentration levels in the U.S. Advertising and Marketing Services (A&MS) industry using publicly released data that have been largely ignored in past discussions of the industrial organization of this industry, namely those available from the U.S. Census Bureau's quinquennial Economic Census and the Service Annual Survey. We define the A&MS industry in terms of nine sectors, each of which is represented by a separate 5 digit NAICS category. In so doing, we have sought to redress some of the measurement problems surrounding estimates found in the existing literature. Our main findings are threefold. First, in the case of the core and largest sector, Advertising Agencies, firm level concentration as measured by Herfindahl-Hirschman Index (HHI) increased slightly but remained relatively low from 1977 to 2002. All of the HHI estimates readily satisfied the standard widely used to characterize an industry as "unconcentrated." We find mixed support for the hypotheses that the ranks of mid-sized agencies were depleted by ongoing waves of mergers and acquisitions and resulted in a polarized size structure. The size distributions of agency revenue have become more polarized in the sense that over time they appear more skewed, more dispersed, and exhibit greater inequality. The share of total receipts realized by small agencies fell while that of large agencies rose. However, the position of mid-sized agencies appears to have changed little over the period 1977- 2002, as measured by the shares of agencies and receipts they represent. Second, concentration levels in 1997 and 2002 varied across the nine sectors comprising the A&MS industry, but all were within the range generally considered as indicative of a competitive industry. Third, we developed concentration ratios at the level of holding companies (HC's) and find that the four largest HC's captured between a fifth and a quarter of total revenue from the A&MS industry, a share that remained quite stable over the period, 2002-2006. These estimates are lower by an order of magnitude than estimates often cited in the trade press. Reasons for the discrepancy are discussed.

Costs, Institutional Mobility Barriers, and Market Structure: Advertising Agencies as Multiproduct Firms

What accounts for the diversity and limited concentration that has long characterized the organization of the advertising agency industry? This question is addressed by treating an advertising agency as a multiproduct firm. The firm's product line or service mix is defined in terms of the set of different media categories where an agency places the advertising messages which it creates on behalf of its clients. Evidence is presented indicating that the structure of demand and costs in the advertising agency industry conforms to the conditions that MacDonald and Slivinski (1987) showed were required for an industry to sustain an equilibrium with diversified firms. Building on this framework, we formulate a set of three hypotheses relating to the realization of product-specific scale and scope economies. The first two hypotheses posit that given low fixed costs and minimal entry barriers, both media-specific scale and scope economies are available and can be exploited by relatively small-size agencies. The third hypothesis suggests that large agencies may experience diseconomies of scope as a consequence of excessive diversification induced by two pervasive industry institutional phenomena: (i) 'bundling' of agency services to match client demand for a mix of media advertising; and (ii) 'conflict policy' which prohibits an agency from serving competing accounts and operates as a mobility constraint. Utilizing a multiproduct cost function, we estimate media-specific scale and scope economies for a cross-section of 401 U.S. agencies in 1987. The results obtained support the set of three hypotheses outlined above.