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Marginal Effects (marginal + effects)
Selected AbstractsOwnership Concentration and Corporate Performance on the Budapest Stock Exchange: do too many cooks spoil the goulash?CORPORATE GOVERNANCE, Issue 2 2005John S. Earle We examine the impact of ownership concentration on firm performance using panel data for firms listed on the Budapest Stock Exchange, where ownership tends to be highly concentrated and frequently involves multiple blocks. Fixed-effects estimates imply that the size of the largest block increases profitability and efficiency strongly and monotonically, but the effects of total blockholdings are much smaller and statistically insignificant. Controlling for the size of the largest block, point estimates of the marginal effects of additional blocks are negative. The results suggest that the marginal costs of concentration may outweigh the benefits when the increased concentration involves "too many cooks". [source] The Effects of Screening and Monitoring on Credit Rationing of SMEsECONOMIC NOTES, Issue 2 2008Mariarosaria Agostino In this paper, we seek to empirically assess which determinants of the capability and incentives of banks to screen and monitor firms are significant in explaining credit rationing to Italian SMEs. After testing for the presence of non-random selection bias and the potential endogeneity of some determinants of interest, the probit model results we obtain suggest that the average banking size and the multiple banking relationship phenomenon are statistically significant factors affecting credit rationing, presumably through their impact on the aforementioned banks' capability and incentives. Other potential determinants of banks' incentives to monitor and screen, such as local banking competition and firm' capacity to collateralize, are never significant. However, when we split the sample according to the level of competition in credit markets, we find that the estimated marginal effects of all significant determinants of interest are larger in absolute value than those obtained when using the whole sample. [source] The Impact of Welfare Reform on Insurance Coverage before Pregnancy and the Timing of Prenatal Care InitiationHEALTH SERVICES RESEARCH, Issue 4 2007Norma I. Gavin Objective. This study investigates the impact of welfare reform on insurance coverage before pregnancy and on first-trimester initiation of prenatal care (PNC) among pregnant women eligible for Medicaid under welfare-related eligibility criteria. Data Sources. We used pooled data from the Pregnancy Risk Assessment Monitoring System for eight states (AL, FL, ME, NY, OK, SC, WA, and WV) from 1996 through 1999. Study Design. We estimated a two-part logistic model of insurance coverage before pregnancy and first-trimester PNC initiation. The impact of welfare reform on insurance coverage before pregnancy was measured by marginal effects computed from coefficients of an interaction term for the postreform period and welfare-related eligibility and on PNC initiation by the same interaction term and the coefficients of insurance coverage adjusted for potential simultaneous equation bias. We compared the estimates from this model with results from simple logistic, ordinary least squares, and two-stage least squares models. Principal Findings. Welfare reform had a significant negative impact on Medicaid coverage before pregnancy among welfare-related Medicaid eligibles. This drop resulted in a small decline in their first-trimester PNC initiation. Enrollment in Medicaid before pregnancy was independent of the decision to initiate PNC, and estimates of the effect of a reduction in Medicaid coverage before pregnancy on PNC initiation were consistent over the single- and two-stage models. Effects of private coverage were mixed. Welfare reform had no impact on first-trimester PNC beyond that from reduced Medicaid coverage in the pooled regression but separate state-specific regressions suggest additional effects from time and income constraints induced by welfare reform may have occurred in some states. Conclusions. Welfare reform had significant adverse effects on insurance coverage and first-trimester PNC initiation among our nation's poorest women of childbearing age. Improved outreach and insurance options for these women are needed to meet national health goals. [source] Which little piggy goes to market?INTERNATIONAL JOURNAL OF CONSUMER STUDIES, Issue 3 2009Characteristics of US farmers' market shoppers Abstract The growth in farmers' markets in the US has raised questions about whether they are a niche market or appeal to a broader population. Using a simple, random sample of US food shoppers, this study uses a test of means to examine whether there are differences in characteristics between those who shop at farmers' markets and those who do not. A key finding was that there was no significant difference in the level of food expenditures between shoppers and non-shoppers. In addition, a probit model was used to examine the marginal effects of attitudinal, behavioural and demographic variables on the probability of shopping at a farmers' market. The probability was significantly increased by the following: enjoyment and frequency of cooking, being female and the presence of another adult in the household. Income did not significantly influence the probability of shopping at a farmers' market. However, the probability of shopping at a farmers' market was significantly reduced if respondents perceived that cost was the most important characteristic of food. These characteristics imply limited appeal of farmers' markets currently to convenience-oriented, single-person, and single-parent households. [source] Active immunization against leptin fails to affect reproduction and exerts only marginal effects on glucose metabolism in young female goatsJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 7-8 2006H. Sauerwein Summary Approximately 150 days before expected breeding time, 12 female goats (3 months of age) were actively immunized against ovine leptin. Booster injections were given throughout the following year. Control animals (n = 6) were sham-immunized. After the first observed oestrus, a buck was introduced and goats were mated. Blood samples were collected twice weekly and frequent blood sampling series were performed on days ,15, 76, 153 and 286 relative to the first immunization. Nine of the immunized goats developed titres within 3 months and had elevated serum concentrations of leptin compared with controls (p < 0.0001). Hematological parameters and blood chemistry were not affected by the immunization. No differences were detectable in all reproductive parameters recorded. Serum insulin was higher in immunized goats during the frequent blood sampling series of day 287 after the first immunization. Glucose metabolism was investigated during pregnancy using hyperglycaemic and euglycaemic/hyperinsulinaemic clamps. None of the parameters derived from the clamp studies was different (p > 0.05) between the two groups. During the hyperglycaemic clamp there was a trend (p < 0.15) towards increased insulin concentrations in immunized animals whereas glucose infusion rates were not different between the groups. This indicates decreased insulin sensitivity in immunized goats. Our study describes the ontogenesis of serum concentrations of leptin during growth, puberty and first pregnancy and parturition for the caprine species. The effects of the immunization were not detectable or only marginal and the approach aimed at therefore not effective to investigate leptin action in detail. [source] High school completion and future youth unemployment: new evidence from High School and BeyondJOURNAL OF APPLIED ECONOMETRICS, Issue 1 2006Professor Mingliang Li In this paper, I provide new evidence from High School and Beyond (HSB) on the effects of compulsory attendance on high school completion and future youth unemployment. I develop Bayesian estimation approaches to the simultaneous equation model with ordered probit and two-limit censored regression and the bivariate duration model, accounting for the heterogeneity in returns to education and the nonlinearity in the effects of compulsory attendance. I find substantial variability in returns to education across schools and evidence of diminishing marginal effects of compulsory attendance on high school completion. The simulation results suggest that increasing the compulsory attendance age raises the probability of completing high school and reduces the proportion of time the individuals are unemployed. These effects are much more pronounced for disadvantaged students but less pronounced for advantaged students, suggesting the potential effects of compulsory attendance on reducing the inequality in education and employment. Copyright © 2005 John Wiley & Sons, Ltd. [source] Pikeperch Sander lucioperca trapped between niches: foraging performance and prey selection in a piscivore on a planktivore dietJOURNAL OF FISH BIOLOGY, Issue 4 2008A. Persson The foraging behaviour of planktivorous pikeperch Sander lucioperca during their first growing season was analysed. Field data showed that S. lucioperca feed on extremely rare prey at the end of the summer, suggesting the presence of a bottleneck. In experiments, foraging ability of planktivorous S. lucioperca was determined when fish were feeding on different prey types (Daphnia magna or Chaoborus spp.) and sizes (D. magna of lengths 1 or 2·5 mm) when they occurred alone. From these results, the minimum density requirement of each prey type was analysed. The energy gain for three different foraging strategies was estimated; a specialized diet based on either large D. magna or Chaoborus spp. or a generalist diet combining both prey types. Prey value estimates showed that Chaoborus spp. should be the preferred prey, assuming an energy maximizing principle. In prey choice experiments, S. lucioperca largely followed this principle, including D. magna in the diet only when the density of the Chaoborus spp. was below a threshold value. Splitting the foraging bout into different sequences, however, resulted in a somewhat different pattern. During an initial phase, S. lucioperca captured both prey as encountered and then switched to Chaoborus spp. if prey density was above the threshold level. The prey selection observed was mainly explained by sampling behaviour and incomplete information about environmental quality, whereas satiation only had marginal effects. It was concluded that the observed diet based on rare prey items was in accordance with an optimal foraging strategy and may generate positive growth in the absence of prey fish in suitable sizes. [source] Behavioral tradeoffs when dispersing across a patchy landscapeOIKOS, Issue 2 2005Patrick A. Zollner A better understanding of the behavior of dispersing animals will assist in determining the factors that limit their success and ultimately help improve the way dispersal is incorporated into population models. To that end, we used a simulation model to investigate three questions about behavioral tradeoffs that dispersing animals might face: (i) speed of movement against risk of predation, (ii) speed of movement against foraging, and (iii) perceptual range against risk of predation. The first investigation demonstrated that dispersing animals can generally benefit by slowing from maximal speed to perform anti-predatory behavior. The optimal speed was most strongly influenced by the disperser's energetic reserves, the risk of predation it faced, the interaction between these two parameters, and the effectiveness of its anti-predatory behavior. Patch arrangement and the search strategy employed by the dispersers had marginal effects on this tradeoff relative to the above parameters. The second investigation demonstrated that slowing movement to forage during dispersal may increase success and that optimum speed of dispersal was primarily a function of the dispersing animal's energetic reserves, predation risk, and their interaction. The richness (density of food resources) of the interpatch matrix and the patch arrangement had relatively minor impacts on how much time a dispersing animal should spend foraging. The final investigation demonstrated animals may face tradeoffs between dispersing under conditions that involve a low risk of predation but limit their ability to perceive distant habitat (necessitating more time spent searching for habitat) and conditions that are inherently more risky but allow animals to perceive distant habitat more readily. The precise nature of this tradeoff was sensitive to the form of the relationship between predation risk and perceptual range. Our overall results suggest that simple depictions of these behavioral tradeoffs might suffice in spatially explicit population models. [source] Technical Efficiency in a Semi-Formal Financial Sector: The Case of Mexico,OXFORD BULLETIN OF ECONOMICS & STATISTICS, Issue 1 2007Julia Paxton Abstract The semi-formal financial sector in Mexico is playing an increasingly important role in serving a largely poor, rural clientele. A stochastic frontier with non-monotonic marginal effects [Wang, Journal of Productivity Analysis (2002), Vol. 18, pp. 241,253] reveals a wide disparity in technical efficiency levels among 190 Mexican semi-formal financial intermediaries. The results show that technology, average loan size, rural outreach and institutional age are all positively associated with technical efficiency. The marginal effects vary widely and, in some cases, the effects are non-monotonic over percentile groups. The results indicate that strengthening younger, technologically undeveloped financial institutions will have the strongest marginal benefit in revitalizing the rural financial sector. [source] Differential indirect effects of two plant viruses on an invasive and an indigenous whitefly vector: implications for competitive displacementANNALS OF APPLIED BIOLOGY, Issue 3 2009J. Liu Abstract The role of vector,begomovirus,plant interactions in the widespread invasion by some members of the whitefly species complex Bemisia tabaci is poorly understood. The invasive B biotype of B. tabaci entered China in the late 1990s and had become the predominant or only biotype of the whitefly in many regions of the country by 2005,2006. Meanwhile epidemics of begomoviruses have been observed in many crops including tomato for which Tomato yellow leaf curl China virus (TYLCCNV) and Tomato yellow leaf curl virus (TYLCV) have been identified as two major disease-causing agents. Here, we conducted laboratory experiments to compare the performance of the invasive B and indigenous ZHJ1 whitefly biotypes on uninfected, TYLCCNV-infected and TYLCV-infected plants of tomato cv. Hezuo903, a cultivar that has been widely cultivated in many regions of China. The infection of tomato plants by either of the viruses had no or only marginal effects on the development, survival and fecundity of the B biotype. In contrast, survival and fecundity of the ZHJ1 biotype were significantly reduced on virus-infected plants compared to those on uninfected plants. Populations of the B biotype on uninfected and TYLCCNV-infected plants increased at similar rates, whereas population increase of the ZHJ1 biotype on TYLCCNV-infected plants was affected adversely. These asymmetric responses to virus infection of tomato plants between the B and ZHJ1 biotypes are likely to offer advantages to the B biotype in its invasion and displacement of the indigenous biotype. [source] Identification of Interacting Genes in Genome-Wide Association Studies Using a Model-Based Two-Stage ApproachANNALS OF HUMAN GENETICS, Issue 5 2010Zhaogong Zhang Summary In this paper, we propose a two-stage approach based on 17 biologically plausible models to search for two-locus combinations that have significant joint effects on the disease status in genome-wide association (GWA) studies. In the two-stage analyses, we only test two-locus joint effects of SNPs that show modest marginal effects. We use simulation studies to compare the power of our two-stage analysis with a single-marker analysis and a two-stage analysis by using a full model. We find that for most plausible interaction effects, our two-stage analysis can dramatically increase the power to identify two-locus joint effects compared to a single-marker analysis and a two-stage analysis based on the full model. We also compare two-stage methods with one-stage methods. Our simulation results indicate that two-stage methods are more powerful than one-stage methods. We applied our two-stage approach to a GWA study for identifying genetic factors that might be relevant in the pathogenesis of sporadic Amyotrophic Lateral Sclerosis (ALS). Our proposed two-stage approach found that two SNPs have significant joint effect on sporadic ALS while the single-marker analysis and the two-stage analysis based on the full model did not find any significant results. [source] Evaluating the Ability of Tree-Based Methods and Logistic Regression for the Detection of SNP-SNP InteractionANNALS OF HUMAN GENETICS, Issue 3 2009M. García-Magariños Summary Most common human diseases are likely to have complex etiologies. Methods of analysis that allow for the phenomenon of epistasis are of growing interest in the genetic dissection of complex diseases. By allowing for epistatic interactions between potential disease loci, we may succeed in identifying genetic variants that might otherwise have remained undetected. Here we aimed to analyze the ability of logistic regression (LR) and two tree-based supervised learning methods, classification and regression trees (CART) and random forest (RF), to detect epistasis. Multifactor-dimensionality reduction (MDR) was also used for comparison. Our approach involves first the simulation of datasets of autosomal biallelic unphased and unlinked single nucleotide polymorphisms (SNPs), each containing a two-loci interaction (causal SNPs) and 98 ,noise' SNPs. We modelled interactions under different scenarios of sample size, missing data, minor allele frequencies (MAF) and several penetrance models: three involving both (indistinguishable) marginal effects and interaction, and two simulating pure interaction effects. In total, we have simulated 99 different scenarios. Although CART, RF, and LR yield similar results in terms of detection of true association, CART and RF perform better than LR with respect to classification error. MAF, penetrance model, and sample size are greater determining factors than percentage of missing data in the ability of the different techniques to detect true association. In pure interaction models, only RF detects association. In conclusion, tree-based methods and LR are important statistical tools for the detection of unknown interactions among true risk-associated SNPs with marginal effects and in the presence of a significant number of noise SNPs. In pure interaction models, RF performs reasonably well in the presence of large sample sizes and low percentages of missing data. However, when the study design is suboptimal (unfavourable to detect interaction in terms of e.g. sample size and MAF) there is a high chance of detecting false, spurious associations. [source] Testing Association with Interactions by Partitioning Chi-SquaresANNALS OF HUMAN GENETICS, Issue 1 2009Y. Yang Summary Gene-gene interaction plays an important role in association studies for complex diseases. There have been different approaches to incorporating gene-gene interactions in candidate gene or genome-wide association studies, especially for those genes with no marginal effects but with interaction effects. However, there is no general agreement on how interaction should be tested and how main effects and interaction effects act on a significance signal. In this paper, we propose a test of the null hypothesis of no association in terms of interaction effects for two unlinked loci, which is a 4 degrees of freedom (df) chi-square for two SNPs. The test, derived by contrasting inter-locus disequilibrium measures between cases and controls, can be viewed as the interaction component of the total Pearson chi-square. The remaining portion of the total chi-square can also be used for association analysis, which emphasizes main effects. Simulation studies show that in most situations our interaction test is similar in power to the test based on a logistic regression model but has more power when the genes have no marginal effects. Results also show that single-locus marginal tests can lose much power if interaction effects dominate main effects. For some specific genetic models, the interaction test may be further partitioned into four 1-df chi-squares for individual interaction effect. The interaction pattern can best be demonstrated by the 1-df chi-square components. Simulation results show that there is substantial power gain if interaction patterns are properly incorporated in association analysis. [source] Role of Education in Cigarette Smoking: An Analysis of Malaysian Household Survey Data,ASIAN ECONOMIC JOURNAL, Issue 1 2009Andrew K.G. Tan D12; I21 Heckman's sample selection model is used to examine the role of education on household purchase decisions and expenditures of tobacco products in Malaysia. Results of the marginal effects of education, segmented by ethnic and gender groups, suggest that education decreases the probability, conditional levels and unconditional levels of tobacco expenditures amongst Malaysian households. Specifically, an additional year of education of the household head, irrespective of ethnic or gender considerations, decreases smoking probability by 1.5 percent. However, the negative effect of education seems to be higher for Chinese (US$1.07) than Malay (US$0.26) households in terms of conditional expenditures. Furthermore, education significantly decreases conditional tobacco expenditures within male-headed households. [source] Determinants of Recidivism in Paroled Queensland Prisoners: A Comparative Analysis of Custodial and Socioeconomic CharacteristicsAUSTRALIAN ECONOMIC PAPERS, Issue 3 2000Andrew Worthington A multinomial ordered probit model is used to predict post-release performance in a sample of Queensland prisoners released between January 1992 and December 1994. Post-release performance is defined in terms of the seriousness of parole breaches and/or reoffences over the length of the parole period or until April 1996. The paper examines the statistical significance of a number of custodial and socioeconomic variables on the likelihood of a parole breach or re-offence. Factors analysed include family composition, age, occupation, ethnicity, the number of events in custody, the number of prison violations and the length of sentence of the most recent custodial episode. All other things being equal, the marginal effects of readmission with respect to the set of explanatory variables varies markedly according to whether readmission is through a parole breach or through actual recidivist behaviour. [source] Speaking versus typing: a case-study of the effects of using voice-recognition software on academic correspondenceBRITISH JOURNAL OF EDUCATIONAL TECHNOLOGY, Issue 1 2003James Hartley This paper contributes to the discussion about the effects of new technology on writing by assessing whether or not an experienced writer's style of writing changes when a new technology is introduced. 14 typed word-processed letters from ES to JH were compared with 14 dictated word-processed letters from ES after he had changed to using a voice-recognition system (Dragon Naturally Speaking). The results showed that, although there were large differences between the methods and experience of writing with the two technologies, there were no significant differences between the average letter lengths, numbers of paragraphs written and number of sentences used in each group of letters. Nor were there any significant differences in terms of readability, or typographical and grammatical errors. However, the dictated letters did have significantly shorter sentences, significantly fewer particularly long sentences (ie, those containing more than 50 words), and used the first-person pronoun more frequently. The overall results thus indicate that using the voice-recognition software had only marginal effects upon the written products, despite the fact that it had a strong effect on ES's experience of the writing process. [source] | |||||||||||||