Estimating multiway error-components models with correlated effects in Stata

I derive new estimators and tests of correlated effects for the (possibly) unbalanced multiway error component model (ECM), extending existing results in various aspects. The results by Kang (1985) on specification tests, who extended Hausman and Taylor (1981) and Mundlak (1978) to the two-way balanced model, emerge as particular cases of the present analysis. Davis (2002), who extends the analysis of Wansbeek and Kaptein (1989) to the multiway unbalanced model does not consider the cases of either correlated effects or specification tests. I also uncover new algebraic properties of the multiway ECM covariance matrix that prove useful for both computational and analytical purposes. Finally, I provide some examples using Stata.

Two-Way Automata Making Choices Only at the Endmarkers

The question of the state-size cost for simulation of two-way nondeterministic automata (2NFAs) by two-way deterministic automata (2DFAs) was raised in 1978 and, despite many attempts, it is still open. Subsequently, the problem was attacked by restricting the power of 2DFAs (e.g., using a restricted input head movement) to the degree for which it was already possible to derive some exponential gaps between the weaker model and the standard 2NFAs. Here we use an opposite approach, increasing the power of 2DFAs to the degree for which it is still possible to obtain a subexponential conversion from the stronger model to the standard 2DFAs. In particular, it turns out that subexponential conversion is possible for two-way automata that make nondeterministic choices only when the input head scans one of the input tape endmarkers. However, there is no restriction on the input head movement. This implies that an exponential gap between 2NFAs and 2DFAs can be obtained only for unrestricted 2NFAs using capabilities beyond the proposed new model. As an additional bonus, conversion into a machine for the complement of the original language is polynomial in this model. The same holds for making such machines self-verifying, halting, or unambiguous. Finally, any superpolynomial lower bound for the simulation of such machines by standard 2DFAs would imply LNL. In the same way, the alternating version of these machines is related to L =? NL =? P, the classical computational complexity problems.Comment: 23 page

Single Bunch Instabilities in FCC-ee

FCC-ee is a high luminosity lepton collider with a centre-of-mass energy from 91 to 365 GeV. Due to the machine parameters and pipe dimensions, collective effects due to electromagnetic fields produced by the interaction of the beam with the vacuum chamber can be one of the main limitations to the machine performance. In this frame, an impedance model is required to analyze these instabilities and to find possible solutions for their mitigation. This paper will present the contributions of specific machine components to the total impedance budget and their effects on the beam stability. Single bunch instability thresholds will be estimated in both transverse and longitudinal planes

New wine in new bottles: Visualizing the progression over time of the epidemics of tobacco smoking and obesity through the use of modified population pyramids

Tobacco smoking and obesity greatly contribute to premature death and disease in developed countries. In order to measure the extent to which these risk factors affect a population, as well as to describe the progression of these epidemics over time, routine surveillance of the prevalence of obesity and smoking is carried out by international organizations, national departments of health, and statistical offices. To this end, summary measures—like age-standardized rates, and tabular and graphical representations, such as maps—are used. In this study, we argue that population pyramids, a widely used demographic tool, may be easily adapted to provide relevant visual information for public health purposes. By means of two juxtaposed histograms, one for each gender, population pyramids show either the proportion or the actual number of subjects in each age and gender subgroup. We suggest that stratifying each bar of the two histograms according to ordinal categories of the health condition or risk factor examined may provide useful details on the relationship between this condition or factor and key demographic variables like age and gender. In addition, the actual number of exposed subjects can be immediately read from the graph. We therefore built a statistical routine with Stata to create modified population-pyramid plots separately for overweight/obese and current/former smoker. Data were derived from five National Health Interview Surveys carried out in Italy between 1983 and 2005. For each survey, data on age, gender, smoking status, height, and weight were extracted for subjects aged 20–99. Age and gender-specific prevalence rates of overweight/obese, and of current/former/never smoker were computed and applied to population estimates performed by the Italian national statistical institute (ISTAT). The resulting estimated numbers of underweight/normal weight/overweight/obese individuals and of former/current/never smokers were used to create the modified population pyramids. In conclusion, modified population pyramids may contribute to assessing the impact of risk factors on a population in absolute terms, to evaluating how these risk factors are distributed by age and gender, and to assessing how the age and gender distribution of these risk factors changes over time.

Organizing for innovation: R&D projects, activities and partners

We explore how R&D project characteristics condition the governance of an R&D project and its individual activities. Prior literature has tried to understand the factors - both at the industry and at the firm level - that influence the way in which firms partner for innovation. In this paper, through the analysis of detailed data from a subsidiary of STMicroelectronics, we identify the main drivers of partner selection for innovation. Partnering or contracting with universities for innovation is common practice for developing new -original- knowledge, as opposed to applying existing knowledge to a problem. But firms are more reluctant to partner, especially with other firms, when that knowledge directly enhances their competitiveness. However, conditional on cooperation, partners are more likely to act individually when the project is strategically important. Contracting for innovation to universities or research centers, as opposed to partnering, happens for more experimental projects, where highly original knowledge is developed, and typically early on in the project.Innovation strategy; Technological innovation; R&D projects' organization; Partner selection;