Multilevel Mixed Linear Models for Survival Data

For the analysis of correlated survival data mixed linear models are useful alternatives to frailty models. By their use the survival times can be directly modelled, so that the interpretation of the fixed and random effects is straightforward. However, because of intractable integration involved with the use of marginal likelihood the class of models in use has been severely restricted. Such a difficulty can be avoided by using hierarchical-likelihood, which provides a statistically efficient and fast fitting algorithm for multilevel models. The proposed method is illustrated using the chronic granulomatous disease data. A simulation study is carried out to evaluate the performance.     

Elder mistreatment in urban India: a community based study

This study examined the extent and correlates of elder mistreatment among 400 community dwelling older adults aged 65 and above in Chennai, India. The prevalence rate of mistreatment was 14%. Chronic verbal abuse was the most common followed by financial abuse and the rate of physical abuse and neglect was similar. Among the mistreated, exactly half of them had experienced more than one type of mistreatment (multifaceted-mistreatment). With the exception of financial abuse, a significantly greater number of women experienced verbal and physical abuse as well as neglect compared to men. Adult children, daughters-in-law, spouses, and sons-in-law were the prominent perpetrators. The mistreated older adults were more depressed and less satisfied with life than those who were not mistreated. Logistic regression analysis revealed gender, social support, and subjective rating of physical health as significant factors associated with abuse.     

A Standardized Normal-Laplace Mixture Distribution Fitted to Symmetric Implied Volatility Smiles

This article proposes to use a standardized version of the normal-Laplace mixture distribution for the modeling of tail-fatness in an asset return distribution and for the fitting of volatility smiles implied by option prices. Despite the fact that only two free parameters are used, the proposed distribution allows arbitrarily high kurtosis and uses one shape parameter to adjust the density function within three standard deviations for any specified kurtosis. For an asset price model based on this distribution, the closed-form formulas for European option prices are derived, and subsequently the volatility smiles can be easily obtained. A regression analysis is conducted to show that the kurtosis, which is commonly used as an index of tail-fatness, is unable to explain the smiles satisfactorily under the proposed model, because the additional shape parameter also significantly accounts for the deviations revealed in smiles. The effectiveness of the proposed parsimonious model is demonstrated in the practical examples where the model is fitted to the volatility smiles implied by the NASDAQ market traded foreign exchange options.     

Stability and Change in an Urban Homeless Population

Few studies have produced the over-time observational data needed to draw valid conclusions about changes in urban homeless populations during the 1980s. One place for which such data exist is Nashville, Tennessee. An ongoing series of enumerations lends little support to Nashvillians' perception that the number of homeless in their city is growing rapidly. Enumeration results also (1) contradict expectations regarding the rise of "new homeless" groups and (2) show two types of spatial redistribution--from indoor to outdoor and core to peripheral locations--to be under way. The applicability of the enumeration methodology to other communities is discussed, as are the discrepancies between purported and measured demographic changes in homelessness.     

Optimal design of synthetic np control chart based on median run length

The synthetic np chart is a combination of the np sub-chart and the conforming run length sub-chart. A procedure for the optimal design of the synthetic np chart is provided by minimizing the out-of-control median run length (MRL). The comparative results show that the synthetic np chart performs better than the corresponding standard np chart for detecting process shifts in the fraction non conforming, in terms of the MRL. An example is given to illustrate the operation of the synthetic np chart.     

Which Voluntary Organizations Function as Schools of Democracy? Civic Engagement in Voluntary Organizations and Political Participation

VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations - Voluntary organizations have been praised as “schools of democracy” that promote citizens’ political...     

Mobile Phone Usage Preferences: The Contributing Factors of Personality,Social Anxiety and Loneliness

Psychological factors and social relationships are important components that influence an individual’s communication style. This paper aims to examine the association of personality factors, social anxiety (SA) and loneliness with mobile phone (MP) usage preferences on the basis of voice calling and text messaging. Malaysian MP users (N = 187) completed four questionnaires (Mobile Phone Usage Questionnaire, Big Five Inventory, Interaction Anxiousness Scale and UCLA Loneliness Scale) on paper or online via a web-link. Multiple regression analyses revealed that personality, SA and loneliness broadly predicted preferences for voice calling or text messaging. Further analyses examining the predictability of time spent on voice calls/text messaging and number of people called/exchanged text messages also revealed some significant findings in regards to the openness-to-experience personality dimension, loneliness and SA. The findings of this research have important implications to tailoring the delivery of psychological services to individuals diagnosed with chronic loneliness and SA.     

Methods for estimating relative risk in studies of common binary outcomes

Studying the effect of exposure or intervention on a dichotomous outcome is very common in medical research. Logistic regression (LR) is often used to determine such association which provides odds ratio (OR). OR often overestimates the effect size for prevalent outcome data. In such situations, use of relative risk (RR) has been suggested. We propose modifications in Zhang and Yu and Diaz-Quijano methods. These methods were compared with stratified Mantel Haenszel method, LR, log binomial regression (LBR), Zhang and Yu method, Poisson/Cox regression, modified Poisson/Cox regression, marginal probability method, COPY method, inverse probability of treatment weighted LBR, and Diaz-Quijano method. Our proposed modified Diaz-Quijano (MDQ) method provides RR and its confidence interval similar to those estimated by modified Poisson/Cox and LBRs. The proposed modifications in Zhang and Yu method provides better estimate of RR and its standard error as compared to Zhang and Yu method in a variety of situations with prevalent outcome. The MDQ method can be used easily to estimate the RR and its confidence interval in the studies which require reporting of RRs. Regression models which directly provide the estimate of RR without convergence problems such as the MDQ method and modified Poisson/Cox regression should be preferred.