Inferences on the shape parameter of the gamma distribution and Cramer-Rao lower bounds from censored data

This dissertation is presented in publication form and consists of two articles. The first article considers inferential procedures on the shape parameter of a gamma distribution from censored sampling. Moments for the statistic T = log(x̅r/x͠r) are found and used to derive a two-moment chi-square approximation for T. This approximation is then used for testing, estimating, and setting confidence bounds on the shape parameter of a gamma distribution. The second article concerns the Cramér-Rao lower bounds for the variances of estimators, where the estimators are based on censored data. Convenient techniques are derived to evaluate the lower bounds in the presence or absence of nuisance parameters --Abstract, page iii

Observations on Short-Term and Long-Range Plans for Technology Transfer to State and Local Governments

Efforts to apply the scientific and technical resources of the hundreds of Federal laboratories to the solving of technical problems of industry, State and local governments have met with only limited success. In part, this is because of lack of understanding of how to bridge the gap between highly sophisticated sources of technical information and users less skilled in technical pursuits. The National Science Foundation, in cooperation with many of the major public interest groups, has been initiating and evaluating a number of networks to bridge the gap. It has also worked with State and local governments to improve their capabilities to define clearly their technical needs and seek solutions

Analyzing the Determinants of the Matching Public School Teachers to Jobs: Estimating Compensating Differentials in Imperfect Labor Markets

Although there is growing recognition of the contribution of teachers to students' educational outcomes, there are large gaps in our understanding of how teacher labor markets function. Most research on teacher labor markets use models developed for the private sector. However, markets for public school teachers differ in fundamental ways from those in the private sector. Collective bargaining and public decision making processes set teacher salaries. Thus it is unlikely that wages adjust quickly to equilibrate the supply and demand for worker and job attributes. The objective of this paper is to develop and estimate a model that more accurately characterizes the institutional features of teacher labor markets. The approach is based on a game-theoretic two-sided matching model and the estimation strategy employs the method of simulated moments. With this combination, we are able to estimate how factors affect the choices of individual teachers and hiring authorities, as well as how these choices interact to determine the equilibrium allocation of teachers across jobs. Even though this paper focuses on worker-job match within teacher labor markets, many of the issues raised and the empirical framework employed are relevant in other settings where wages are set administratively or, more generally, do not clear the pertinent markets for job and worker attributes.

Recruiting Effective Math Teachers: How Do Math Immersion Teachers Compare?: Evidence from New York City

School districts often struggle to recruit and retain effective math teachers. Alternative-route certification programs aim to expand the pool of teachers available; however, many alternate routes have not been able to attract large numbers of teacher candidates with undergraduate degrees in math. In response, some districts, including Baltimore, Philadelphia, Washington D.C., and New York City, have developed alternative programs with a math immersion component to recruit candidates who do not have undergraduate majors in math. Such programs provide potential math teachers with intensive math preparation to meet state certification requirements while, at the same time maintaining an early-entry approach in which individuals who have not completed a teacher preparation program can become qualified to teach with only five to seven weeks of coursework and practice teaching. Four years since its inception, the New York City Teacher Fellows Math Immersion program supplies 50 percent of all new certified math teachers to New York City public schools. In this study, we find that Math Immersion teachers have stronger academic qualifications than their College Recommending (traditionally certified) peers, although they have weaker qualifications than Teach for America teachers. However, despite stronger general academic qualifications Math Immersion teachers produce somewhat smaller gains in math achievement for middle school math students than do College Recommending teachers and substantially smaller gains than do Teach for America teachers.

How Teacher Turnover Harms Student Achievement

Researchers and policymakers often assume that teacher turnover harms student achievement, but recent evidence calls into question this assumption. Using a unique identification strategy that employs grade-level turnover and two classes of fixed-effects models, this study estimates the effects of teacher turnover on over 600,000 New York City 4th and 5th grade student observations over 5 years. The results indicate that students in grade-levels with higher turnover score lower in both ELA and math and that this effect is particularly strong in schools with more low-performing and black students. Moreover, the results suggest that there is a disruptive effect of turnover beyond changing the composition in teacher quality.

Who Leaves? Teacher Attrition and Student Achievement

Almost a quarter of entering public-school teachers leave teaching within their first three years. High attrition would be particularly problematic if those leaving were the more able teachers. The goal of this paper is estimate the extent to which there is differential attrition based on teachers' value-added to student achievement. Using data for New York City schools from 2000–2005, we find that first-year teachers whom we identify as less effective at improving student test scores have higher attrition rates than do more effective teachers in both low-achieving and high-achieving schools. The first-year differences are meaningful in size; however, the pattern is not consistent for teachers in their second and third years. For teachers leaving low-performing schools, the more effective transfers tend to move to higher achieving schools, while less effective transfers stay in lower-performing schools, likely exacerbating the differences across students in the opportunities they have to learn.

The Narrowing Gap in New York City Teacher Qualifications and its Implications for Student Achievement in High-Poverty Schools

The gap between the qualifications of New York City teachers in high-poverty schools and low-poverty schools has narrowed substantially since 2000. Most of this gap-narrowing resulted from changes in the characteristics of newly hired teachers, and largely has been driven by the virtual elimination of newly hired uncertified teachers coupled with an influx of teachers with strong academic backgrounds in the Teaching Fellows program and Teach for America. The improvements in teacher qualifications, especially among the poorest schools, appear to have resulted in improved student achievement. By estimating the effect of teacher attributes using a value-added model, the analyses in this paper predict that observable qualifications of teachers resulted in average improved achievement for students in the poorest decile of schools of .03 standard deviations, about half the difference between being taught by a first year teacher and a more experienced teacher. If limited to teachers who are in the first or second year of teaching, where changes in qualifications are greatest, the gain equals two-thirds of the first-year experience effect.

Hepatic encephalopathy: a neurochemical, neuroanatomical, and neuropsychological study.

Hepatic encephalopathy (HE) is normally diagnosed by neuropsychological (NP) tests, which are not very specific and do not reveal the underlying pathology. Magnetic resonance imaging (MRI) and spectroscopy (MRS) of the brain offer alternative and possibly more specific markers for HE. These methods were applied in conjunction with NP testing in order to determine their usefulness in the identification of HE and to understand the pathogenesis of HE more clearly. MR imaging and spectroscopy examinations, in addition to a battery of 15 NP tests, were administered to investigate 31 patients awaiting liver transplantation and 23 healthy controls. MR image intensities from the globus pallidus region were calculated and normalized to those of the thalamus. Absolute concentrations and ratios with respect to creatine (Cr) of several metabolites were computed from MR spectra. The MR data were correlated with the results of NP tests. The patients showed impairment in NP tests of attention and visuospatial and verbal fluency. In T1-weighted MRI, the relative intensity of the globus pallidus with respect to that of the thalamus region was significantly elevated in patients and correlated(negatively) with three NP tests (Hooper, FAS, and Trails B). The absolute concentrations of myo-inositol (mI) and choline (Ch) were significantly reduced in three brain regions. In addition, the absolute concentrations of glutamine (Gln) and combined glutamate and glutamine (Glx) were increased in all three locations, with Gln increase being significant in all areas while that of Glx only in the occipital white matter. In summary, this study partially confirms a hypothesized mechanism of HE pathogenesis, an increased synthesis of glutamine by brain glutamate in astrocytes due to excessive blood ammonia, followed by a compensatory loss of myo-inositol to maintain astrocyte volume homeostasis. It also indicates that the hyperintensity observed in globus pallidus could be used as complementary to the NP test scores in evaluating the mental health of HE patients

Teacher Preparation and Student Achievement

There are fierce debates over the best way to prepare teachers. Some argue that easing entry into teaching is necessary to attract strong candidates, while others argue that investing in high quality teacher preparation is the most promising approach. Most agree, however, that we lack a strong research basis for understanding how to prepare teachers. This paper is one of the first to estimate the effects of features of teachers' preparation on teachers' value-added to student test score performance in math and English Language Arts. Our results indicate variation across preparation programs in the average effectiveness of the teachers they are supplying to New York City schools. In particular, preparation directly linked to practice appears to benefit teachers in their first year.