Use of Pseudo-observations in the Goodness-of-Fit Test for Gray's Time-Varying Coefficients Model

Survival analysis has been used to estimate underlying survival or failure probabilities and to estimate the effects of covariates on survival times. The Cox proportional hazards regression model is the most commonly used approach. However, in practical situations, the assumption of proportional hazards (PH) is often violated. The assumption does not hold, for example, in the presence of the time-varying effect of a covariate. Several methods have been proposed to estimate this time-varying effect via a time-varying coefficient. The Gray time-varying coefficients model (TVC) is an extension of the Cox PH model that employs penalized spline functions to estimate time-varying coefficients. Currently, there is no method available to assess the overall goodness-of-fit for the Gray TVC model. In this study, we propose a method based on pseudo-observations. By using pseudo-observations, we are able to calculate residuals for all individuals at all time points. This avoids concerns with the presence of censoring and allows us to apply the residual plots used in general linear regression models to assess the overall goodness of fit for censored survival regression models. Perme and Andersen used the pseudo-observations method to assess the fit for the Cox PH model. We extend their method to assess the fit for the Gray TVC model and illustrate how we applied this approach to assess the fit for a model that predicts posttransplant survival probability among children who were under the age of 12 years, had end-stage liver disease, and underwent liver transplantation between January 2005 and June 2010.The method has significant public health impact. The Cox PH model is the most cited regression method in medical research. When data violate the PH assumption, The Gray TVC model or an alternative should be used in order to obtain unbiased estimates on survival function and give correct inference on the relationship between potential covariates and survival. The proposed goodness-of-fit test offers a tool to investigate how well the model fits the data. If results show a lack of fit, further modification for the model is necessary in order to obtain more accurate estimates

Use of Pseudo-observations in the Goodness-of-Fit Test for Gray\u27s Time-Varying Coefficients Model

Background The Cox proportional hazards (PH) regression model is the most common method to estimate underlying survival or failure probabilities and to estimate the effects of covariates on survival times. In Cox PH models, the regression coefficients are assumed constant over time. However, if covariate effects vary over time, alternative models which do not necessarily assume proportionality are needed. Method We proposed the Gray’s time-varying coefficient (TVC) method based on pseudo-observation. By using pseudo-observations, pseudo-residuals were calculated and plotted against the estimated survival rates at each of the nine selected time points, then were used to evaluate the goodness-of-fit of the Gray’s model. We applied this method to assess the fit for a model that predicts post-transplant survival probability among children who were under the age of 12 years, had end-stage liver disease, and underwent liver transplantation between January 2005 and June 2010. Result For Gray’s TVC model, through the first time point and the sixth time point, pseudo residual plots are around zero, while pseudo residual plots show slight departure at small values of estimated survival rate through the seventh time point and the ninth time point. Since the pseudo residual plots stay around zero at each time point without any significant departure or tendency, we can conclude that Gray’s model shows a good fit in estimating survival function at each time point. The results from this real liver transplantation data demonstrate that the final Gray’s model shows a good fit in estimating post-transplant survival. Conclusion When data violate the PH assumption, the Gray TVC model or an alternative should be used to obtain unbiased estimates on survival function and give correct inference on the relationship between potential covariates and survival. The proposed goodness-of-fit test offers a tool to investigate how well the model fits the data

Risk of Recurrent Falls after Indoor and Outdoor Falls in the Elderly

Background: Falls are the most common and serious health problems of the elderly. The primary goal of the study is to determine whether risk for recurrent indoor and outdoor falls differ by type of previous falls and by gender. Method: We analyzed data on falls collected in the MOBILIZE Boston prospective cohort study of community-dwelling women and men aged 65 years or older. The participants were followed for up to 4.3 years (median=2.3y). Logistic regression models, clustered by participant, were performed to estimate the probability of a subsequent indoor or outdoor fall after any fall, indoor fall, and outdoor fall. Natural log transformed time since the most recent any fall, time since the most recent indoor fall, and time since the most recent outdoor fall were used to predict probabilities of a subsequent fall of each type. Result: Among 502 participants who reported at least one fall during the follow-up, 330 had at least one reccurent fall during the follow-up period. Men and women differed in their tendencies to fall recurrently as well as in their response to an outdoor fall. Median time to the recurrent any fall since the most recent any fall was 9 weeks (IQR=22) for men and 17 weeks (IQR=30) for women [p= Conclusion: Falls, especially outdoor falls, may have different implications for the subsequent fall risks of men vs. women. Further study should examine whether outdoor falls may be an indicator of robustness for elderly women but for frailty in elderly men

Recent Advance in Colon Capsule Endoscopy: What’s New?

Colon capsule endoscopy (CCE) is a relatively new diagnostic procedure for patients with suspected colonic diseases. This convenient, noninvasive method enables the physician to explore the entire colon without significant discomfort to the patient. However, while CCE can be performed painlessly without bowel air insufflation, the need for vigorous bowel preparation and other technical limitations exist. Due to such limitations, CCE has not replaced conventional colonoscopy. In this review, we discuss historical and recent advances in CCE including technical issues, ideal bowel preparation, indications and contraindications and highlight further technical advancements and clinical studies which are needed to develop CCE as a potential diagnostic tool

Creating Store and Community-Level Feedback Reports for Food Establishments to Support Nutrition Environment Improvement

INTRODUCTION. The availability of healthy options in food stores is important to healthy eating and obesity prevention. The Health Statistics and Geography Lab at UMass Medical School is conducting longitudinal surveys to determine the availability of healthy food in food stores throughout the state of Massachusetts as part the Community Transformation Grant and Mass in Motion initiatives. Providing feedback to store proprietors and managers as well as community workers is an important component to support community environmental interventions. METHODS. The Community Nutrition Environment Evaluation Data System (C-NEEDS) was developed for food environment surveillance. C-NEEDS takes into account seasonal and geographic variations in food supplies, cultural relevance, and USDA dietary recommendations. Since May 2012, nearly 1300 food stores throughout Massachusetts have been surveyed and analyzed. Healthy Food Availability Index (HFAI) is calculated for each store (range: 0 to 56), with a higher score indicating greater availability of healthy items. REPORTS. Store-level reports are provided to proprietors and managers of individual food stores in conjunction with community workers. The reports provide HFAI scores for the store for the current year, previous year(s), if available, comparing to the average scores of similar stores within the same community. Community workers and proprietors of food stores can use the store-level reports to determine areas of need and appropriate intervention methodology. Community-level feedback reports provide information on average scores, by store type, for their community as well as for communities of similar size and socio-demographic status. They can be used to compare community HFAI to comparable communities as well as track change in scores over time. DISCUSSION. Providing feedback to community workers and food store owners is an essential aspect of community enviornment interventions. The information contained in the C-NEEDS feedback reports provides benchmarks for both store owners and communities to achieve

Misclassification of Healthy Eating Based on Food Frequency Questionnaires and 24-hour Dietary Recalls in Older Men and Women

OBJECTIVE: To examine the agreement in nutrient intake and alternative healthy eating indices (AHEI) between a self-administered Food Frequency Questionnaire (FFQ) and 24-hour recall (24HR) measurements of diet by gender among older adults. METHODS: This is a cross-sectional observational study of 105 men and 99 women aged 65 and older living in urban and rural neighborhoods in Worcester County. Participants were queried on diet using both FFQ and 24HR. The healthy eating classification was compared between the two instruments by gender. RESULTS: For men, the mean±SD of AHEI total score was 48.2±12.3 based on FFQ versus 34.7±10.2 based on 24HR. For women, the mean±SD was 47.9±10.1 based on FFQ versus 36.1±10.0 based on 24HR. Using 32 as the cutoff (40% of maximum AHEI score), 9% of men and 7% of women were classified as eating unhealthy based on the FFQ, versus 47% of men and 38% of women based on 24HR. Compared to women, men had larger 24HR to FFQ discrepancies in the nuts and vegetable protein subscore and white/red meat ratio, and smaller discrepancy in alcohol beverages subscore. CONCLUSION: Agreements between FFQ and 24HR-based measures of diet quality were roughly comparable between men and women, though slightly better for women than men. Compared to 24HR, the FFQ tended to underestimate the proportions of older men and women classified as eating unhealthy and misclassified more men than women. Such limitations should be considered when the FFQ is used to study healthy eating in older age

Low roll-off of efficiency at high current density in phosphorescent organic light emitting diodes

The authors demonstrate that the reduction of quantum efficiency with increasing current density in phosphorescent light emitting diodes (PhOLEDs) is related to the formation of excitons in hole transporting layer based on the analysis of emission spectra and exciton formation zone. Low roll-off of efficiency in a PhOLED was achieved using dual emitting layers (D-EMLs) by confining the exciton formation near the interface between the emitting layers. The external quantum efficiency was maintained almost constant up to 22 mA/cm2 (10 000 cd/m2) by adopting the D-EMLs in Ir(ppy)3 based PhOLEDs, resulting in high external quantum efficiency (ext=13.1%) at high luminance.This work was supported by the Ministry of Commerce, Industry and Energy of Korea through the OLED center, Samsung SDI, Dongwoo Finechem, and CKC Program

Racial Disparities in In-hospital Mortality and Discharge Disposition among Trauma Patients in Massachusetts

Background: Population-based data on trauma care are important to a solid understanding of racial disparities in the care and outcomes of trauma patients. Methods: Data on inpatient hospitalizations for trauma were obtained from the Massachusetts (MA) Statewide Trauma Registry which conducts annual census of trauma-related hospitalizations in MA. This analysis included patients who were MA residents and admitted to a MA hospital between 2008 and 2010, and 15 years and older at the time of admission. Patients were grouped as non-Hispanic white, non-Hispanic black, Hispanic, Asian, and other or unknown race. Injury severity, discharge disposition and mortality of the first hospitalization of the patients were compared among the groups while adjusting for sex, age and severity. Results: The data were from 23,666 patients with a mean age of 63.8 years. The patients included 51.8% women, 86.1% whites, 4.3% blacks, 5.6% Hispanics, 1.2% Asians and 2.7% other or unknown races. In total, 597 (2.52%) died in the hospital. Asians and other races had higher risk for death (OR=2.96, p Conclusions: Remarkable racial/ethnic disparities in inhospital mortality and discharge dispositions were seen among trauma patients in MA. The determinants of the disparities and related policy implications are under investigation by a study supported by the National Institute on Minority Health and Health Disparities