Modelling zero-inflated count data when exposure varies: with an application to tumor counts)

This paper is concerned with the analysis of zero-inflated count data when time of exposure varies. It proposes a modified zero-inflated count data model where the probability of an extra zero is derived from an underlying duration model with Weibull hazard rate. The new model is compared to the standard Poisson model with logit zero inflation in an application to the effect of treatment with thiotepa on the number of new bladder tumors.

Pre-Election Positions and Voting Behaviour in Parliament: Consistency among Swiss MPs

This article examines the determinants of positional incongruence between pre-election statements and post-election behaviour in the Swiss parliament between 2003 and 2009. The question is examined at the individual MP level, which is appropriate for dispersion-of-powers systems like Switzerland. While the overall rate of political congruence reaches about 85%, a multilevel logit analysis detects the underlying factors which push or curb a candidate's propensity to change his or her mind once elected. The results show that positional changes are more likely when (1) MPs are freshmen, (2) individual voting behaviour is invisible to the public, (3) the electoral district magnitude is not small, (4) the vote is not about a party's core issue, (5) the MP belongs to a party which is located in the political centre, and (6) if the pre-election statement dissents from the majority position of the legislative party group. Of these factors, the last one is paramount.

The Psychological Outcome of Religious Coping with Stressful Life Events in a Swiss Sample of Church Attendees

Background: Recent research suggested thatreligious coping, based on dispositional religiousness and spirituality (R/S), is an important modulating factor in the process of dealing with adversity. In contrast to the United States, the effect of R/S on psychological adjustment to stress is a widely unexplored area in Europe. Methods: We examined a Swiss sample of 328 church attendees in the aftermath of stressful life events to explore associations of positive or negative religious coping with the psychological outcome. Applying a cross-sectional design, we used Huber’s Centrality Scale to specify religiousness and Pargament’s measure of religious coping (RCOPE) for the assessment of positive and negative religious coping. Depressive symptoms and anxiety as outcome variables were examined by the Brief Symptom Inventory. The Stress-Related Growth Scale and the Marburg questionnaire for the assessment of well-being were used to assess positive outcome aspects. We conducted Mann-Whitney tests for group comparisons and cumulative logit analysis for the assessmentof associations of religious coping with our outcome variables. Results: Both forms of religious coping were positively associated with stress-related growth (p < 0.01). However, negative religious coping additionally reduced well-being (p = 0.05, β = 0.52, 95% CI = 0.27–0.99) and increased anxiety (p = 0.02, β = 1.94, 95% CI = 1.10–3.39) and depressive symptoms (p = 0.01, β = 2.27, 95% CI = 1.27–4.06). Conclusions: The effects of religious coping on the psychological adjustment to stressful life events seem relevant. These findings should be confirmed in prospective studies.

Now You See it, Now You Don't: Why Do Real Estate Agents Withhold Available Houses from Black Customers?

Potential home buyers may initiate contact with a real estate agent by asking to see a particular advertised house. This paper asks whether an agent's response to such a request depends on the race of the potential buyer or on whether the house is located in an integrated neighborhood. We build on previous research about the causes of discrimination in housing by using data from fair housing audits, a matched-pair technique for comparing the treatment of equllay qualified black and white home buyers. However, we shift the focus from differences in the treatment of paired buyers to agent decisions concerning an individual housing unit using a sample of all houses seen during he 1989 Housing Discrimination study. We estimate a random effect, multinomial logit model to explain a real estate agent's joint decisions concerning whether to show each unit to a black auditor and to a white auditor. We find evidence that agents withhold houses in suburban, integrated neighborhoods from all customers (redlining), that agents' decisions to show houses in integrated neighborhoods are not the same for black and white customers (steering), and that the houses agents show are more likely to deviate from the initial request when the customeris black than when the customer is white. These deviations are consistent with the possibility that agents act upon the belief that some types of transactions are relatively unlikely for black customers (statistical discrimination).

Shirking and Motivation in Firms: Survey Evidence on Worker Attitudes

In an extensive national survey, 82.7% of the respondents report that they are very likely to keep an agreement to work hard if they agreed to, even if it was almost impossible for their employer to monitor them. Based on mean responses, the rank order of motivations in descending importance is: moral, intrinsic, peer-pressure, and positive incentives. Respondents also report that fairness considerations are important and that they are especially likely to keep agreements to do a good job with honest employers. Logit analysis indicates that increases in moral and intrinsic motivations increase the likelihood of keeping agreements to provide effort. The evidence suggests that we need to re-examine a foundational assumption underlying the theory of the firm.

Logistic regression models for ordinal response: A study of self-efficacy in colorectal cancer screening

The ordinal logistic regression models are used to analyze the dependant variable with multiple outcomes that can be ranked, but have been underutilized. In this study, we describe four logistic regression models for analyzing the ordinal response variable. ^ In this methodological study, the four regression models are proposed. The first model uses the multinomial logistic model. The second is adjacent-category logit model. The third is the proportional odds model and the fourth model is the continuation-ratio model. We illustrate and compare the fit of these models using data from the survey designed by the University of Texas, School of Public Health research project PCCaSO (Promoting Colon Cancer Screening in people 50 and Over), to study the patient’s confidence in the completion colorectal cancer screening (CRCS). ^ The purpose of this study is two fold: first, to provide a synthesized review of models for analyzing data with ordinal response, and second, to evaluate their usefulness in epidemiological research, with particular emphasis on model formulation, interpretation of model coefficients, and their implications. Four ordinal logistic models that are used in this study include (1) Multinomial logistic model, (2) Adjacent-category logistic model [9], (3) Continuation-ratio logistic model [10], (4) Proportional logistic model [11]. We recommend that the analyst performs (1) goodness-of-fit tests, (2) sensitivity analysis by fitting and comparing different models.^

HPV vaccine coverage in Texas counties: An application of multilevel, small area estimation

Health departments, research institutions, policy-makers, and healthcare providers are often interested in knowing the health status of their clients/constituents. Without the resources, financially or administratively, to go out into the community and conduct health assessments directly, these entities frequently rely on data from population-based surveys to supply the information they need. Unfortunately, these surveys are ill-equipped for the job due to sample size and privacy concerns. Small area estimation (SAE) techniques have excellent potential in such circumstances, but have been underutilized in public health due to lack of awareness and confidence in applying its methods. The goal of this research is to make model-based SAE accessible to a broad readership using clear, example-based learning. Specifically, we applied the principles of multilevel, unit-level SAE to describe the geographic distribution of HPV vaccine coverage among females aged 11-26 in Texas.^ Multilevel (3 level: individual, county, public health region) random-intercept logit models of HPV vaccination (receipt of ≥ 1 dose Gardasil® ) were fit to data from the 2008 Behavioral Risk Factor Surveillance System (outcome and level 1 covariates) and a number of secondary sources (group-level covariates). Sampling weights were scaled (level 1) or constructed (levels 2 & 3), and incorporated at every level. Using the regression coefficients (and standard errors) from the final models, I simulated 10,000 datasets for each regression coefficient from the normal distribution and applied them to the logit model to estimate HPV vaccine coverage in each county and respective demographic subgroup. For simplicity, I only provide coverage estimates (and 95% confidence intervals) for counties.^ County-level coverage among females aged 11-17 varied from 6.8-29.0%. For females aged 18-26, coverage varied from 1.9%-23.8%. Aggregated to the state level, these values translate to indirect state estimates of 15.5% and 11.4%, respectively; both of which fall within the confidence intervals for the direct estimates of HPV vaccine coverage in Texas (Females 11-17: 17.7%, 95% CI: 13.6, 21.9; Females 18-26: 12.0%, 95% CI: 6.2, 17.7).^ Small area estimation has great potential for informing policy, program development and evaluation, and the provision of health services. Harnessing the flexibility of multilevel, unit-level SAE to estimate HPV vaccine coverage among females aged 11-26 in Texas counties, I have provided (1) practical guidance on how to conceptualize and conduct modelbased SAE, (2) a robust framework that can be applied to other health outcomes or geographic levels of aggregation, and (3) HPV vaccine coverage data that may inform the development of health education programs, the provision of health services, the planning of additional research studies, and the creation of local health policies.^

The prevalence of periodontal disease in Mexican American vs European American elderly in three distinct socio-economic communities in San Antonio, Texas

Purpose of the Study: This study evaluated the prevalence of periodontal disease between Mexican American elderly and European American elderly residing in three socio-economically distinct neighborhoods in San Antonio, Texas. ^ Study Group: Subjects for the original protocol were participants of the Oral Health: San Antonio Longitudinal Study of Aging (OH: SALSA), which began with National Institutes of Health (NIH) funding in 1993 (M.J. Saunders, PI). The cohort in the study was the individuals who had been enrolled in Phases I and III of the San Antonio Heart Study (SAHS). This SAHS/SALSA sample is a community-based probability sample of Mexican American and European American residents from three socio-economically distinct San Antonio neighborhoods: low-income barrio, middle-income transitional, and upper-income suburban. The OH: SALSA cohort was established between July 1993 and May 1998 by sampling two subsets of the San Antonio Heart Study (SAHS) cohort. These subsets included the San Antonio Longitudinal Study of Aging (SALSA) cohort, comprised of the oldest members of the SAHS (age 65+ yrs. old), and a younger set of controls (age 35-64 yrs. old) sampled from the remainder of the SAHS cohort. ^ Methods: The study used simple descriptive statistics to describe the sociodemographic characteristics and periodontal disease indicators of the OH: SALSA participants. Means and standard deviations were used to summarize continuous measures. Proportions were used to summarize categorical measures. Simple m x n chi square statistics was used to compare ethnic differences. A multivariable ordered logit regression was used to estimate the prevalence of periodontal disease and test ethnic group and neighborhood differences in the prevalence of periodontal disease. A multivariable model adjustment for socio-economic status (income and education), gender, and age (treated as confounders) was applied. ^ Summary: In the unadjusted and adjusted model, Mexican American elderly demonstrated the greatest prevalence for periodontitis, p < 0.05. Mexican American elderly in barrio neighborhoods demonstrated the greatest prevalence for severe periodontitis, with unadjusted prevalence rates of 31.7%, 22.3%, and 22.4% for Mexican American elderly barrio, transitional, and suburban neighborhoods, respectively. Also, Mexican American elderly had adjusted prevalence rates of 29.4%, 23.7%, and 20.4% for barrio, transitional, and suburban neighborhoods, respectively. ^ Conclusion: This study indicates that the prevalence of periodontal disease is an important oral health issue among the Mexican American elderly. The results suggest that the socioeconomic status of the residential neighborhood increased the risk for severe periodontal disease among the Mexican American elderly when compared to European American elderly. A viable approach to recognizing oral health disparities in our growing population of Mexican American elderly is imperative for the provision of special care programs that will help increase the quality of care in this minority population.^

Renal Cryoablation: Investigation of Periprocedural Visualization Tools and Treatment Response Quantification

Cryoablation for small renal tumors has demonstrated sufficient clinical efficacy over the past decade as a non-surgical nephron-sparing approach for treating renal masses for patients who are not surgical candidates. Minimally invasive percutaneous cryoablations have been performed with image guidance from CT, ultrasound, and MRI. During the MRI-guided cryoablation procedure, the interventional radiologist visually compares the iceball size on monitoring images with respect to the original tumor on separate planning images. The comparisons made during the monitoring step are time consuming, inefficient and sometimes lack the precision needed for decision making, requiring the radiologist to make further changes later in the procedure. This study sought to mitigate uncertainty in these visual comparisons by quantifying tissue response to cryoablation and providing visualization of the response during the procedure. Based on retrospective analysis of MR-guided cryoablation patient data, registration and segmentation algorithms were investigated and implemented for periprocedural visualization to deliver iceball position/size with respect to planning images registered within 3.3mm with at least 70% overlap and a quantitative logit model was developed to relate perfusion deficit in renal parenchyma visualized in verification images as a result of iceball size visualized in monitoring images. Through retrospective study of 20 patient cases, the relationship between likelihood of perfusion loss in renal parenchyma and distance within iceball was quantified and iteratively fit to a logit curve. Using the parameters from the logit fit, the margin for 95% perfusion loss likelihood was found to be 4.28 mm within the iceball. The observed margin corresponds well with the clinically accepted margin of 3-5mm within the iceball. In order to display the iceball position and perfusion loss likelihood to the radiologist, algorithms were implemented to create a fast segmentation and registration module which executed in under 2 minutes, within the clinically-relevant 3 minute monitoring period. Using 16 patient cases, the average Hausdorff distance was reduced from 10.1mm to 3.21 mm with average DSC increased from 46.6% to 82.6% before and after registration.

Factors that influence the decision to produce exportables in the Chilean agricultural sector

This study analyzes there lative importance of the factors that influence the decision to produce for foreign markets in the Chilean agricultural sector. Using data obtained from personal interviews with 368 farmers, the market/production decision was estimated using a multinomial logit model. Three market/production alternatives were analyzed: production aimed for the external market, production for the internal market but with expectations of being exported, and production targeted only for the internal market. Marginal effects, odds ratios and predicted probabilities were used to identify the relevance of each variable. The results showed that a producer that is male, with a higher educational level, that does not own the land, but rents it, whose farm has irrigation and is located in an area that has a high concentration of exporting producers, will have a high probability of producing exportables. However, the factor that has the highest impact on producing for the external market is the geographic concentration of exporting producers, that is, an export spillover effect. Indeed, when the concentration change from 0 to its maximum (0.26), the odds of producing exportables rather than producing traditional products increases by a factor of 70 (against a factor of 10 in the case of irrigation).

La aspiración de /s/ en el español rioplatense : Tango vs. rock

En el español rioplatense, la aspiración de /s/ preconsonántica es la norma (Terrell 1978), mientras que el debilitamiento en final de palabra ante vocal o pausa parece estar estigmatizado (Fontanella 1973; Barrios 2002). Los hablantes de este dialecto, sin embargo, tienen en principio la capacidad de controlar la tasa de debilitamiento para acercarse a diferentes normas de pronunciación, en especial en contextos de carácter formal como la interpretación de una canción. La principal hipótesis de este trabajo es que, ante una situación como esa, es esperable hallar una variación en la tasa de aspiración según cuál sea el género musical interpretado, lo cual se enlaza con resultados de estudios sociolingüísticos sobre la música popular (Trudgill 1983; Simpson 1999). En nuestro caso, el análisis se lleva a cabo sobre un corpus de 17 canciones agrupadas en dos géneros (tango y rock), y gira en torno a la figura del cantante y compositor Andrés Calamaro. El número total de realizaciones de /s/ preconsonántica relevados asciende a 701, de los cuales 393 corresponden a grabaciones de tango y 308 a grabaciones de rock. Para cada género, comparamos la tasa de aspiración de /s/ preconsonántica en las interpretaciones de Calamaro con las mismas canciones cantadas por diversos intérpretes (tanto de tango como de rock). Los resultados obtenidos a partir de la transcripción fonética fueron sometidos a un análisis de regresión múltiple (modelo logit), el cual reveló que las variables 'género' e 'intérprete' predicen significativamente controlar por factores de carácter fonético (punto y modo de articulación de la consonante siguiente, acentuación de la sílaba en la cual aparece la /s/ implosiva), posicional (/s/ intermedia o final de palabra) y gramatical (/s/ como marca verbal o de plural), y son también reinterpretados utilizando la lógica del modelo de reglas variables (varbrul). Los resultados de este trabajo indican que la /s/ preconsonántica es aspirada significativamente más en el tango que en el rock. También se verifica que, al interpretar tangos, Andrés Calamaro aspira significativamente menos dicho sonido que los cantantes que grabaron las versiones originales analizadas. Sin embargo, el propio Calamaro utiliza de manera significativamente más frecuente la aspiración cuando interpreta tangos que cuando interpreta canciones de rock. En conclusión, los resultados parecen respaldar la teoría de que los cantantes se acercan a una pronunciación más local cuando interpretan un género vernáculo (tango) y a una norma pan-hispánica cuando interpretan un género de carácter internacional (rock)

La aspiración de /s/ en el español rioplatense : Tango vs. rock

En el español rioplatense, la aspiración de /s/ preconsonántica es la norma (Terrell 1978), mientras que el debilitamiento en final de palabra ante vocal o pausa parece estar estigmatizado (Fontanella 1973; Barrios 2002). Los hablantes de este dialecto, sin embargo, tienen en principio la capacidad de controlar la tasa de debilitamiento para acercarse a diferentes normas de pronunciación, en especial en contextos de carácter formal como la interpretación de una canción. La principal hipótesis de este trabajo es que, ante una situación como esa, es esperable hallar una variación en la tasa de aspiración según cuál sea el género musical interpretado, lo cual se enlaza con resultados de estudios sociolingüísticos sobre la música popular (Trudgill 1983; Simpson 1999). En nuestro caso, el análisis se lleva a cabo sobre un corpus de 17 canciones agrupadas en dos géneros (tango y rock), y gira en torno a la figura del cantante y compositor Andrés Calamaro. El número total de realizaciones de /s/ preconsonántica relevados asciende a 701, de los cuales 393 corresponden a grabaciones de tango y 308 a grabaciones de rock. Para cada género, comparamos la tasa de aspiración de /s/ preconsonántica en las interpretaciones de Calamaro con las mismas canciones cantadas por diversos intérpretes (tanto de tango como de rock). Los resultados obtenidos a partir de la transcripción fonética fueron sometidos a un análisis de regresión múltiple (modelo logit), el cual reveló que las variables 'género' e 'intérprete' predicen significativamente controlar por factores de carácter fonético (punto y modo de articulación de la consonante siguiente, acentuación de la sílaba en la cual aparece la /s/ implosiva), posicional (/s/ intermedia o final de palabra) y gramatical (/s/ como marca verbal o de plural), y son también reinterpretados utilizando la lógica del modelo de reglas variables (varbrul). Los resultados de este trabajo indican que la /s/ preconsonántica es aspirada significativamente más en el tango que en el rock. También se verifica que, al interpretar tangos, Andrés Calamaro aspira significativamente menos dicho sonido que los cantantes que grabaron las versiones originales analizadas. Sin embargo, el propio Calamaro utiliza de manera significativamente más frecuente la aspiración cuando interpreta tangos que cuando interpreta canciones de rock. En conclusión, los resultados parecen respaldar la teoría de que los cantantes se acercan a una pronunciación más local cuando interpretan un género vernáculo (tango) y a una norma pan-hispánica cuando interpretan un género de carácter internacional (rock)

La aspiración de /s/ en el español rioplatense : Tango vs. rock

En el español rioplatense, la aspiración de /s/ preconsonántica es la norma (Terrell 1978), mientras que el debilitamiento en final de palabra ante vocal o pausa parece estar estigmatizado (Fontanella 1973; Barrios 2002). Los hablantes de este dialecto, sin embargo, tienen en principio la capacidad de controlar la tasa de debilitamiento para acercarse a diferentes normas de pronunciación, en especial en contextos de carácter formal como la interpretación de una canción. La principal hipótesis de este trabajo es que, ante una situación como esa, es esperable hallar una variación en la tasa de aspiración según cuál sea el género musical interpretado, lo cual se enlaza con resultados de estudios sociolingüísticos sobre la música popular (Trudgill 1983; Simpson 1999). En nuestro caso, el análisis se lleva a cabo sobre un corpus de 17 canciones agrupadas en dos géneros (tango y rock), y gira en torno a la figura del cantante y compositor Andrés Calamaro. El número total de realizaciones de /s/ preconsonántica relevados asciende a 701, de los cuales 393 corresponden a grabaciones de tango y 308 a grabaciones de rock. Para cada género, comparamos la tasa de aspiración de /s/ preconsonántica en las interpretaciones de Calamaro con las mismas canciones cantadas por diversos intérpretes (tanto de tango como de rock). Los resultados obtenidos a partir de la transcripción fonética fueron sometidos a un análisis de regresión múltiple (modelo logit), el cual reveló que las variables 'género' e 'intérprete' predicen significativamente controlar por factores de carácter fonético (punto y modo de articulación de la consonante siguiente, acentuación de la sílaba en la cual aparece la /s/ implosiva), posicional (/s/ intermedia o final de palabra) y gramatical (/s/ como marca verbal o de plural), y son también reinterpretados utilizando la lógica del modelo de reglas variables (varbrul). Los resultados de este trabajo indican que la /s/ preconsonántica es aspirada significativamente más en el tango que en el rock. También se verifica que, al interpretar tangos, Andrés Calamaro aspira significativamente menos dicho sonido que los cantantes que grabaron las versiones originales analizadas. Sin embargo, el propio Calamaro utiliza de manera significativamente más frecuente la aspiración cuando interpreta tangos que cuando interpreta canciones de rock. En conclusión, los resultados parecen respaldar la teoría de que los cantantes se acercan a una pronunciación más local cuando interpretan un género vernáculo (tango) y a una norma pan-hispánica cuando interpretan un género de carácter internacional (rock)

Survey on economic assessment of the improvement of the quality of environment: the case of the fight against floods in Cotonou (Benin Living Standard Survey)

This study aims to analyze households' attitude toward flood risk in Cotonou in the sense to identify whether they are willing or not to leave the flood-prone zones. Moreover, the attitudes toward the management of wastes and dirty water are analyzed. The data used in this study were obtained from two sources: the survey implemented during March 2011 on one hundred and fifty randomly selected households living in flood-prone areas of Cotonou, and Benin Living Standard Survey of 2006 (Part relative to Cotonou on 1,586 households). Moreover, climate data were used in this study. Multinomial probability model is used for the econometric analysis of the attitude toward flood risk. While the attitudes toward the management of wastes and dirty water are analyzed through a simple logit. The results show that 55.3% of households agreed to go elsewhere while 44.7% refused [we are better-off here (10.67%), due to the proximity of the activities (19.33), the best way is to build infrastructures that will protect against flood and family house (14.67%)]. The authorities have to rethink an alternative policy to what they have been doing such as building socio-economic houses outside Cotonou and propose to the households that are living the areas prone to inundation. Moreover, access to formal education has to be reinforced.

Migration and Wellbeing at the Lower Echelons of the Economy: A Study of Delhi Slums

This paper based on a primary survey of households (2004-05) in the slum clusters of Delhi examines whether migrants are likely to experience upward mobility in their place of destination or alternatively, if they merely transfer their poverty from rural areas to large cities. First, a simple bifurcation of population in terms of poor and non-poor sub-groups is examined along with the incidence of poverty across different categories of occupations and non-workers. Then, an explanation of the variations in per capita expenditure across households is provided, and a binomial logit model (poor/non-poor) is developed identifying the variables which raise (or reduce) the probability of being non-poor (or poor). Next, an estimate of the wellbeing (deprivation) index is derived from factor analysis of a large number of variables including demographic and economic aspects of households. Empirical findings suggest that while duration of migration and the wellbeing index do not have a definite relationship, migrant households who have been in the city for a very long time have a higher wellbeing index on average than those who migrated in the last ten years. This tends to support the view that migrants do not merely transfer rural poverty to urban areas, and further that population mobility yields improvement in the living standard, if only in the very long term. Implementation of "employment-cum-shelter" support schemes in the urban areas may contribute to their wellbeing.