Task-Specific Experience and Task-Specific Talent: Decomposing the Productivity of High School Teachers

We use administrative panel data to decompose worker performance into components relating to general talent, task-specific talent, general experience, and task-specific experience. We consider the context of high school teachers, in which tasks consist of teaching particular subjects in particular tracks. Using the timing of changes in the subjects and levels to which teachers are assigned to provide identifying variation, we show that much of the productivity gains to teacher experience estimated in the literature are actually subject-specific. By contrast, very little of the variation in the permanent component of productivity among teachers is subject-specific or level-specific. Counterfactual simulations suggest that maximizing the value of task-specific experience could produce nearly costless efficiency gains on the order of .02 test score standard deviations

Interpretation of the Cosmological Metric

The cosmological Robertson-Walker metric of general relativity is often said to have the consequences that (1) the recessional velocity $v$ of a galaxy at proper distance $\ell$ obeys the Hubble law $v=H\ell$, and therefore galaxies at sufficiently great distance $\ell$ are receding faster than the speed of light $c$; (2) faster than light recession does not violate special relativity theory because the latter is not applicable to the cosmological problem, and because ``space itself is receding'' faster than $c$ at great distance, and it is velocity relative to local space that is limited by $c$, not the velocity of distant objects relative to nearby ones; (3) we can see galaxies receding faster than the speed of light; and (4) the cosmological redshift is not a Doppler shift, but is due to a stretching of photon wavelength during propagation in an expanding universe. We present a particular Robertson-Walker metric (an empty universe metric) for which a coordinate transformation shows that none of these interpretation necessarily holds. The resulting paradoxes of interpretation lead to a deeper understanding of the meaning of the cosmological metric.Comment: REVTeX 4, 20 pages, accepted for publication in Am. J. Phys. Comments: edited version that will appear in the Am. J. Phy

A spot check of the status of music education of grades four, five and six in the elementary schools of Massachusetts as of the year 1956-57.

Thesis (Ed.M.)--Boston Universit

The Design of Intervention Trials Involving Recurrent and Terminal Events

The final publication (Wu, Longyang, and Richard J. Cook. "The Design of Intervention Trials Involving Recurrent and Terminal Events." Statistics in Biosciences 5(2) (2013): 261-285) is available at Springer via http://dx.doi.org/10.1007/s12561-013-9083-zClinical trials are often designed to assess the effect of therapeutic interventions on the incidence of recurrent events in the presence of a dependent terminal event such as death. Statistical methods based on multistate analysis have considerable appeal in this setting since they can incorporate changes in risk with each event occurrence, a dependence between the recurrent event and the terminal event, and event-dependent censoring. To date, however, there has been limited development of statistical methods for the design of trials involving recurrent and terminal events. Based on the asymptotic distribution of regression coefficients from a multiplicative intensity Markov regression model, we derive sample size formulas to address power requirements for both the recurrent and terminal event processes. We consider the design of trials for which separate marginal hypothesis tests are of interest for the recurrent and terminal event processes and deal with both superiority and non-inferiority tests. Simulation studies confirm that the designs satisfy the nominal power requirements in both settings, and an application to a trial evaluating the effect of a bisphosphonate on skeletal complications is given for illustration.Natural Sciences and Engineering Research Council of Canada (RJC RGPIN 155849, JFL RGPIN 8597); Canadian Institutes for Health Research (FRN 13887); Canada Research Chair (Tier 1) – CIHR funded (950-226626

A case-control study of drug risk factors for age-related macular degeneration.

OBJECTIVE: To investigate the association between age-related macular degeneration (AMD) and exposure to antacids, antithyroids, thyroid hormones, and thiazide diuretics. DESIGN: Matched case-control study. PARTICIPANTS: Population-based participants were selected from the United Kingdom General Practice Research Database. A total of 18,007 people with diagnosed AMD were compared with 86 169 controls matched for age, gender, and general practice. METHODS: Conditional logistic regression was used to determine the association between exposure to each drug group of interest and a diagnosis of AMD, adjusting for relevant confounding variables. MAIN OUTCOME MEASURES: The primary outcome was the odds ratio for the association between exposure to antacids, antithyroids, thyroid hormones, or thiazide diuretics and AMD. Secondary analyses were conducted to assess the effect of recent exposure to the drugs of interest, the total number of prescriptions received, and restricting the data set to participants with more than 2 years of observation time. RESULTS: The crude odds ratios for association between any record of drug exposure and AMD were as follows: 1.34 (95% confidence interval [CI], 1.29-1.39) for antacids; 1.15 (95% CI, 0.92-1.44) for antithyroids; 1.34 (95% CI, 1.29-1.39) for thyroid hormones; and 1.13 (95% CI, 1.08-1.17) for thiazide diuretics. After adjusting for consultation rate, observation time, diabetes, heart failure, hyperlipidemia, cardiovascular drug use, atherosclerosis, hypertension, aspirin use, hormone replacement therapy use, body mass index, alcohol consumption, and smoking, the odds ratios reduced to: 1.06 (95% CI, 1.02-1.10) for antacids, 0.98 (95% CI, 0.78-1.24) for antithyroids, 0.99 (95% CI, 0.92-1.06) for thyroid hormones, and 0.98 (95% CI, 0.94-1.02) for thiazides. Secondary analyses were consistent with these findings for all 4 drug categories. CONCLUSIONS: No association was detected between short- and medium-term use of antithyroids, thyroid hormones, and thiazide diuretics and the risk of AMD. Short- and medium-term use of antacids seems to be associated with a small increase in the risk of this disease. However, this increased risk is likely the result of residual confounding by smoking or uncontrolled confounding resulting from socioeconomic status. No conclusions could be drawn regarding longer-term use of each drug category

Local competition and metapopulation processes drive long-term seagrass-epiphyte population dynamics

It is well known that ecological processes such as population regulation and natural enemy interactions potentially occur over a range of spatial scales, and there is a substantial body of literature developing theoretical understanding of the interplay between these processes. However, there are comparatively few studies quantifying the long-term effects of spatial scaling in natural ecosystems. A key challenge is that trophic complexity in real-world biological communities quickly obscures the signal from a focal process. Seagrass meadows provide an excellent opportunity in this respect: in many instances, seagrasses effectively form extensive natural monocultures, in which hypotheses about endogenous dynamics can be formulated and tested. We present amongst the longest unbroken, spatially explict time series of seagrass abundance published to date. Data include annual measures of shoot density, total above-ground abundance, and associated epiphyte cover from five Zostera marina meadows distributed around the Isles of Scilly, UK, from 1996 to 2011. We explore empirical patterns at the local and metapopulation scale using standard time series analysis and develop a simple population dynamic model, testing the hypothesis that both local and metapopulation scale feedback processes are important. We find little evidence of an interaction between scales in seagrass dynamics but that both scales contribute approximately equally to observed local epiphyte abundance. By quantifying the long-term dynamics of seagrass-epiphyte interactions we show how measures of density and extent are both important in establishing baseline information relevant to predicting responses to environmental change and developing management plans. We hope that this study complements existing mechanistic studies of physiology, genetics and productivity in seagrass, whilst highlighting the potential of seagrass as a model ecosystem. More generally, this study provides a rare opportunity to test some of the predictions of ecological theory in a natural ecosystem of global conservation and economic val

Bone and metal - an orthopaedic perspective on osseointegration of metals

The area of implant osseointegration is of major importance, given the predicted significant rise in the number of orthopaedic procedures and an increasingly ageing population. Osseointegration is a complex process involving a number of distinct mechanisms affected by the implant bulk properties and surface characteristics. Our understanding and ability to modify these mechanisms through alterations in implant design is continuously expanding. The following review considers the main aspects of material and surface alterations in metal implants, and the extent of their subsequent influence on osseointegration. Clinically, osseointegration results in asymptomatic stable durable fixation of orthopaedic implants. The complexity of achieving this outcome through incorporation and balance of contributory factors is highlighted through a clinical case report