Joint modeling of longitudinal outcomes and survival using latent growth modeling approach in a mesothelioma trial

Joint modeling of longitudinal and survival data can provide more efficient and less biased estimates of treatment effects through accounting for the associations between these two data types. Sponsors of oncology clinical trials routinely and increasingly include patient-reported outcome (PRO) instruments to evaluate the effect of treatment on symptoms, functioning, and quality of life. Known publications of these trials typically do not include jointly modeled analyses and results. We formulated several joint models based on a latent growth model for longitudinal PRO data and a Cox proportional hazards model for survival data. The longitudinal and survival components were linked through either a latent growth trajectory or shared random effects. We applied these models to data from a randomized phase III oncology clinical trial in mesothelioma. We compared the results derived under different model specifications and showed that the use of joint modeling may result in improved estimates of the overall treatment effect

Customer emotions in service failure and recovery encounters

Emotions play a significant role in the workplace, and considerable attention has been given to the study of employee emotions. Customers also play a central function in organizations, but much less is known about customer emotions. This chapter reviews the growing literature on customer emotions in employee–customer interfaces with a focus on service failure and recovery encounters, where emotions are heightened. It highlights emerging themes and key findings, addresses the measurement, modeling, and management of customer emotions, and identifies future research streams. Attention is given to emotional contagion, relationships between affective and cognitive processes, customer anger, customer rage, and individual differences

Identifying and interpreting subgroups in health care utilization data with count mixture regression models.

Inpatient care is a large share of total health care spending, making analysis of inpatient utilization patterns an important part of understanding what drives health care spending growth. Common features of inpatient utilization measures such as length of stay and spending include zero inflation, overdispersion, and skewness, all of which complicate statistical modeling. Moreover, latent subgroups of patients may have distinct patterns of utilization and relationships between that utilization and observed covariates. In this work, we apply and compare likelihood-based and parametric Bayesian mixtures of negative binomial and zero-inflated negative binomial regression models. In a simulation, we find that the Bayesian approach finds the true number of mixture components more accurately than using information criteria to select among likelihood-based finite mixture models. When we apply the models to data on hospital lengths of stay for patients with lung cancer, we find distinct subgroups of patients with different means and variances of hospital days, health and treatment covariates, and relationships between covariates and length of stay

Controlling aqueous sorption of humic substances on silica gel by directed alkoxysilyl-derivatization of their functionalities.

In this study we explored a possibility for enhancing aqueous sorption of humic substances (HS) onto hydroxylated surfaces (e.g., silica gel) by increasing modification rate of their most abundant functional groups - carboxyls with mineral-adhesive alkoxysilyl moieties. The synthesis included treatment of dried humic material with 3-aminopropyl trimethoxy silane (APTS) capable of forming amide bonds with carboxyl groups of HS under anhydrous conditions. The reaction was run at six different HS to APTS ratio for achieving different modification degrees of the carboxyl groups in the humic backbone. The obtained derivatives were characterized using elemental analysis, 13C NMR Spectroscopy, Fourier transform infrared spectroscopy, and size exclusion chromatography that confirmed quantitative incorporation of alkoxysilyl-moieties into HS structure. Aqueous adsorption was investigated in 0.028 M phosphate buffer using silica gel as a surrogate for mineral surface. Both distribution coefficients as well adsorption capacities paralleled the amount of alkoxysilyl-moieties incorporated into backbone of the parental HS. The adsorption capacity reached its maximum value of 210 mg of HS per g of SiO2 for the APTS derivative synthesized at the equimolar reagent ratio. This value was comparable to the amount of the same HS immobilized onto the APTS-treated silica gel (265 mg of HS per g of SiO2). Adsorption of alkoxysilyl-derivatives was found to be irreversible under conditions studied. Conclusively, we believe that the directed modification of HS by incorporating alkoxysilyl-moieties is well suited for producing humic derivatives with controllable affinity for aqueous sorption onto hydroxylated surfaces