Who Lives Near Coke Plants and Oil Refineries? An Exploration of the Environmental Inequity Hypothesis

Facility-specific information on pollution was obtained for 36 coke plants and 46 oil refineries in the United States and matched with information on populations surrounding these 82 facilities. These data were analyzed to determine whether environmental inequities were present, whether they were more economic or racial in nature, and whether the racial composition of nearby communities has changed significantly since plants began operations.The Census tracts near coke plants have a disproportionate share of poor and nonwhite residents. Multivariate analyses suggest that existing inequities are primarily economic in nature. The findings for oil refineries are not strongly supportive of the environmental inequity hypothesis. Rank ordering of facilities by race, poverty, and pollution produces limited (although not consistent) evidence that the more risky facilities tend to be operating in communities with above-median proportions of nonwhite residents (near coke plants) and Hispanic residents (near oil refineries). Over time, the racial makeup of many communities near facilities has changed significantly, particularly in the case of coke plants sited in the early 1900s. Further risk-oriented studies of multiple manufacturing facilities in various industrial sectors of the economy are recommended.The authors are all affiliated with the Harvard Center for Risk Analysis     

On the generalized constrained longest common subsequence problems

We investigate four variants of the longest common subsequence problem. Given two sequences X, Y and a constrained pattern P of lengths m, n, and ρ, respectively, the generalized constrained longest common subsequence (GC-LCS) problems are to find a longest common subsequence of X and Y including (or excluding) P as a subsequence (or substring). We propose new dynamic programming algorithms for solving the GC-LCS problems in O(mn ρ) time. We also consider the case where the number of constrained patterns is arbitrary.     

Gender differences in the relationship between walking activity and sleep disturbance among community-dwelling older adult with diabetes in Taiwan

This study explored the gender differences in the relationship between walking activity and sleep disturbances. A cross-sectional study of 201 community-dwelling older adults with diabetes was conducted in southern Taiwan. Using the Taiwanese version of the International Physical Activity Questionnaire, self-administered short version (IPAQ-SS), information on physical activity and sleep disturbance conditions was collected. Among older female adults with diabetes, 54.2% reported sleep disturbance significantly higher than males (38.1%). Logistic regression analysis suggested that for women, in addition to the active group, older adults in the low-active, high-walking group exhibited a significantly lower rate of sleep disturbance than did those who walked less.     

Estimation and selection in linear mixed models with missing data under compound symmetric structure

It is quite appealing to extend existing theories in classical linear models to correlated responses where linear mixed-effects models are utilized and the dependency in the data is modeled by random effects. In the mixed modeling framework, missing values occur naturally due to dropouts or non-responses, which is frequently encountered when dealing with real data. Motivated by such problems, we aim to investigate the estimation and model selection performance in linear mixed models when missing data are present. Inspired by the property of the indicator function for missingness and its relation to missing rates, we propose an approach that records missingness in an indicator-based matrix and derive the likelihood-based estimators for all parameters involved in the linear mixed-effects models. Based on the proposed method for estimation, we explore the relationship between estimation and selection behavior over missing rates. Simulations and a real data application are conducted for illustrating the effectiveness of the proposed method in selecting the most appropriate model and in estimating parameters.     

Maximum likelihood estimation in hazard rate models with a change-point

The problem of estimation of parameters in hazard rate models with a change-point is considered. An interesting feature of this problem is that the likelihood function is unbounded. A maximum likelihood estimator of the change-point subject to a natural constraint is proposed, which is shown to be consistent.The limiting distributions are also derived.     

Global Markov models for eukaryote nucleotide data

We discuss the quite remarkable global Markovian structure of the nucleotides in eukaryotic DNA strands with special emphasis on (i) the similarity property for intra- species chromosomes and (ii) the reversibility property for the two (complementary) strands of a chromosome.     

Can external corporate venturing broaden firm's technological scope? The role of complementary assets

This study applies two theoretical perspectives—resource-based view (RBV) and organizational learning—to explore how a firm's external corporate venturing (CV) influences its technological scope. Using data from 583 electronics and information technology firms in Taiwan for the period from 1997 to 2006, the results indicate that external CVs facilitate an established firm's broadening of its technological scope. Moreover, this study calls into question the idea that a firm's decisions regarding technological scope may be due to a specific factor that governs the extent of technological specialization and diversification. We identify this factor as the complementary assets of established firms. This study, thus, investigates whether complementary assets moderate the relationship between external CV in established firms and those firms’ technological scope. The analytical results also support the idea that increasing investments in specialized complementary assets will urge firms engaged in external CV to concentrate on their technological scope. Therefore, this study addresses the notion that concentrated technological scope is the conjunction of technological capabilities and complementary assets, not determined by either individually.