Effect Of Various Covariates Research Articles

Survival of Commodity Trading Advisors: Systematic vs. Discretionary CTAs

This study investigates the differences in mortality between systematic and discretionary Commodity Trading Advisors, CTAs, over 1994-2009 period, the longest horizon than any encompassed in the literature. This study shows that liquidation is not the same as failure in the CTA industry. New filters are proposed that allow to identify real failures among funds in the graveyard database. By reexamining the attrition rate, this study finds that the real failure rate is in fact 11.1% in the CTA industry lower than the average yearly attrition rate of 17.3%. Secondly this study proposes a new way to classify CTAs, mainly into systematic and discretionary funds and provides detailed analysis of their survival. Systematic CTAs are found to have higher median survival than discretionary, 12 years vs. 8 years. The effect of various covariates including several downside risk measures is investigated in predicting CTA failure. Controlling for performance, HWM, minimum investment, fund age, leverage and lockup, funds with higher downside risk measures have a higher hazard rate. Compared to the other downside risk measures, volatility of returns is less able to predict failure. Fund flows have significant and positive effect on the probability of survival, funds that receive larger inflows are able to survive longer than funds that do not. Finally larger systematic CTAs have the highest probability of survival.

Two-part fractional regression model for the demand for risky assets†

Empirical studies of household portfolio choices are often interested in quantifying the effects of various covariates on the fraction of a household's wealth invested in risky assets such as common stocks. The preferred econometric specification in these studies is the two-limit Tobit model, which can accommodate the fractional nature of the dependent variable. However, it is restrictive, because it assumes that the same data generating process determines both whether households participate in the stock market and the fraction of wealth invested in stocks. This article demonstrates that, in this setting, a two-part version of the fractional response model of Papke and Wooldridge (1996) constitutes an attractive alternative to Tobit by comparing the performance of the two models using data on portfolio choices of Australian households. We find that (1) the Tobit model is rejected by our data in favour of a two-part specification; and (2) marginal effects of covariates on the share of risky assets conditional on participation estimated from Tobit are confounded by the effects of these covariates on the participation decision.

661 RACIAL/ETHNIC DIFFERENCES IN UPPER-TRACT UROTHELIAL CANCER

You have accessJournal of UrologyUrothelial Cancer: Upper Tract Tumors1 Apr 2011661 RACIAL/ETHNIC DIFFERENCES IN UPPER-TRACT UROTHELIAL CANCER GM Monawar Hosain, Myrna Khan, Gilad Amiel, Seth Lerner, David latini, and John Chen GM Monawar HosainGM Monawar Hosain Houston, TX More articles by this author , Myrna KhanMyrna Khan Houston, TX More articles by this author , Gilad AmielGilad Amiel Houston, TX More articles by this author , Seth LernerSeth Lerner Houston, TX More articles by this author , David latiniDavid latini Houston, TX More articles by this author , and John ChenJohn Chen Houston, TX More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2011.02.1591AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Racial/ethnic differences in demographics, cancer stage, treatment and outcome have been observed for many cancer sites. However, data on upper-tract urothelial carcinomas (UTUCs) involving the renal pelvis and ureter are scarce. This study attempted to examine clinical and demographic characteristics and survivals of persons with incident UTUC. METHODS We used a population-based Surveillance, Epidemiology, and End Results (SEER) database from 1988–2007 in the analysis. Race/ethnicity was classified as white, African American (AA) and Hispanics. The study subjects diagnosed with UTUCs were ascertained by ICD-9 codes. We compared racial/ethnic differences in UTUC by gender, age at diagnosis, tumor size, disease stage, lymph node-related data and survival. Chi-square and ANOVA were carried out for analysis of categorical and continuous variables, respectively. Disease-specific survival was calculated, using a Kaplan-Meier model and tested by log-rank test. Cox proportional-hazards models were used to adjust for the effects of various covariates on hazards of death. RESULTS We identified 17,074 UTUC cases in the SEER database from 1988–2007. AA patients were diagnosed at a younger age (67.9 yrs) than whites and Hispanics (71.8 yrs and 69.0 yrs, respectively; p=.004). Whites were less likely to be diagnosed with distant-stage disease (9.0%) compared to AAs and Hispanics (12.7% and 12.5%, respectively; p<.0001), whereas Hispanics were more likely to be diagnosed with larger tumor size (4.4 cm) compared to whites and AAs (3.6 cm and 3.8 cm, respectively). No racial/ethnic differences were observed either in lymph- node removal (17.9%, 17.8 and 17.0% from whites, AAs and Hispanics respectively; p=0.75), or in finding a positive node (4.9%, 4.9% and 5.4% in whites, AAs and Hispanics, respectively; p=0.80). A higher mean number of lymph nodes were examined in Hispanics (6.0) compared to whites (4.8) and AAs (5.3), and it was marginally significant (p=0.07). Cox proportional-hazard model revealed that Hispanics and AAs had a higher risk of dying (HR=1.26, 95% CI=1.12–1.43, p=.0002 and HR=1.10, 95% CI=0.93–1.27, p=.27, respectively) from UTUC than whites. CONCLUSIONS We observed racial/ethnic differences in UTUC cancer-stage distribution and survival as has been seen with other cancers. While no differences were observed for lymph node dissection/examination, we observed that only a small proportion of patients received lymph node dissection across all racial/ethnic groups. © 2011 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 185Issue 4SApril 2011Page: e267 Advertisement Copyright & Permissions© 2011 by American Urological Association Education and Research, Inc.MetricsAuthor Information GM Monawar Hosain Houston, TX More articles by this author Myrna Khan Houston, TX More articles by this author Gilad Amiel Houston, TX More articles by this author Seth Lerner Houston, TX More articles by this author David latini Houston, TX More articles by this author John Chen Houston, TX More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Impact of MDR1 and CYP3A5 on the oral clearance of tacrolimus and tacrolimus-related renal dysfunction in adult living-donor liver transplant patients

The potential influence of the multidrug resistance 1 (MDR1) gene and the cytochrome P450 (CYP) genes, CYP3A4 and CYP3A5, on the oral clearance (CL/F) of tacrolimus in adult living-donor liver transplant patients was examined. Furthermore, the development of renal dysfunction was analyzed in relation to the CYP3A5 genotype. Sixty de novo adult liver transplant patients receiving tacrolimus were enrolled in this study. The effects of various covariates (including intestinal and hepatic mRNA levels of MDR1 and CYP3A4, measured in each tissue taken at the time of transplantation, and the CYP3A5*3 polymorphism) on CL/F during the first 50 days after surgery were investigated with the nonlinear mixed-effects modeling program. CL/F increased linearly until postoperative day 14, and thereafter reached a steady state. The initial CL/F immediately after liver transplantation was significantly affected by the intestinal MDR1 mRNA level (P<0.005). Furthermore, patients carrying the CYP3A5*1 allele in the native intestine, but not in the graft liver, showed a 1.47 times higher (95% confidence interval, 1.17-1.77 times, P<0.005) recovery of CL/F with time than patients having the intestinal CYP3A5*3/*3 genotype. The cumulative incidence of renal dysfunction within 1 year after transplantation, evaluated by the Kaplan-Meier method, was significantly associated with the recipient's but not donor's CYP3A5 genotype (*1/*1 and *1/*3 vs. *3/*3: recipient, 17 vs. 46%, P<0.05; donor, 35 vs. 38%, P=0.81). These findings suggest that the CYP3A5*1 genotype as well as the MDR1 mRNA level in enterocytes contributes to interindividual variation in the CL/F of tacrolimus in adult recipients early after living-donor liver transplantation. Furthermore, CYP3A5 in the kidney may play a protective role in the development of tacrolimus-related nephrotoxicity.

Survival of high tech firms: The effects of diversity of product–market portfolios, patents, and trademarks

High tech firms can mitigate potential risks by diversifying their product–market portfolios. A key research question is how such diversification influences firm survival. A firm exits the market in two ways, specifically, dissolution and acquisition. Here, we model how the diversity of a new firm's product–market portfolio influences the times to both types of exits. Specifically, we allow for interaction effects of the competitive intensity of a firm's environment and the diversity of a firm's product–market portfolio with its patents and trademarks. Using a competing risk hazard model, we estimate the effects of various covariates on the time to exit for 1435 US high tech firms. We observed that a more diverse product–market portfolio, in conjunction with a larger number of patents, hastens the time to a firm's exit by dissolution (9% decrease in survival duration), while in conjunction with a larger number of trademarks, portfolio diversity delays the time to exit by dissolution (12% increase). A more competitive firm environment results in a greater effect on the portfolio's diversity in delaying its exit by dissolution (7% increase). On the other hand, a diverse product–market portfolio, combined with either a larger number of patents or trademarks, hastens the firm's exit by acquisition (19% and 11% decrease respectively).

Birth-spacing patterns in Huaning County, Yunnan Province, PRC: Is the adoption of a small family norm sustainable?

China's family planning programs have emphasized delayed marriage and longer spacing between births. Since 1970, the fertility has declined from 6 to 1.8 births and the mean age at first marriage has gone up but the recommended spacing intervals have not been fully realized. Despite the fertility decline it is being debated among scholars whether China has completed a sustainable demographic transition or not, especially in rural areas. The aim of this study was to analyze trends in the timing and patterns of marriage and childbearing in relation to successive family planning policies. A cluster random sample of 1,336 women aged 15-64 at the time of the survey (2000) was selected in one rural county in Yunnan province. Life-table techniques were used to analyze the cumulative proportion of women marrying and having a certain number of births. Cox's hazard regression model was used to estimate the effects of various covariates on the "hazard" for a woman to have a second birth. Our findings demonstrate how childbearing patterns have changed in the direction of delayed marriage, a decreased interval between first marriage and first child, and significantly longer spacing between the first and second child. This transformation of childbearing patterns corresponds well with the requirements of the policies. Considering the characteristics of Yunnan, it seems likely that the changing fertility behavior has been more influenced by a strictly enforced family planning policy than by societal changes leading to the adoption of a new, smaller family norm.

Population pharmacokinetics and relationship between demographic and clinical variables and pharmacokinetics of gentamicin in neonates.

Population pharmacokinetic parameter estimates were calculated from 725 routine plasma gentamicin concentrations obtained in 177 neonates of 24 to 42 weeks' gestational age in their first week of life. Kel increases and V/W decreases with increasing gestational age. Almost identical results were obtained with iterative two-stage Bayesian fitting (MW\PHARM 3.30) as with a non-parametric maximization algorithm (NPEM2). The effect of various covariates on drug disposition was investigated retrospectively using multiple regression analysis. Predictive power for Kel increases with rising gestational age. For neonates </=28.5 weeks and neonates >28.5 weeks and </=30.9 weeks, the predictive power of the regression equation for Kel was relatively low (r2 respectively 0.270 and 0.364). Better predictivity was found for Kel at gestational ages >30.9 weeks (r2 = 0.482), with gestational age, postnatal age, and Apgar score at 5 minutes being predictors. A very strong correlation existed between volume of distribution and weight (r2 = 0.83). Volume as a function of weight could be described with low predictivity by gestational age and to a lesser degree by Apgar score at 5 minutes (r2 = 0.298). The developed models need appropriate prospective clinical validation.

Spline-based estimation of cure rates: An application to the analysis of breast cancer data

This paper considers the utility of spline approximations of the hazard function for estimation of cure rates from survival data. With this approach, it is possible to assess dissimilar effects of various covariates on the probability of tumor cure and on the timing of the endpoint (death, tumor recurrence, etc.) under study. The usefulness of the approach is illustrated with an application to data on survival of patients treated for breast cancer.

PREDICTION OF RENAL ALLOGRAFT SURVIVAL BY RISE IN SERUM CREATININE (SCr) ABOVE BASELINE (6 MONTH) VALUES

436 Graft loss after the first year remains a major problem in renal transplantation, and is usually heralded by a rise in SCr. We examined the relationship between rise in SCr (compared to 6 months post-op) and subsequent graft survival (GS). Using the 1997 UNOS Center-Specific Report renal database, we identified 45,852 renal transplants (TPs) with followup ≥ 1 yr. GS was estimated using the Kaplan-Meier method. Functional GS was estimated for TPs with SCr rise within specific 0.2 mg/dl increments (○), and for TPs with SCr rise ≥ specific values (•). Deaths with functioning graft were treated as censored observations. The effect of various covariates on GS was examined using the Kaplan-Meier and Cox proportional hazard methods. Results: Median GS (after the first year) for all TPs was 93 mos. 14,833 TPs had SCr rise ≥ 0.4 mg/dl, and SCr ≤ 5.0 at time of SCr rise. Median GS (from time of rise) decreased with increasing SCr rise (graph). Median GS plateaus for rises ≥ 2 mg/dl. For TPs eligible for the current CCTAT chronic rejection intervention trial (SCr rise ≥ 1; SCr ≤ 5.0), median GS was 28 mos. Median GS (after a rise ≥1 mg/dl) was not affected by the interval at which the rise occurred, nor by gender, recipient weight, recipient or donor age, cold ischemia time, or peak PRA. Donor type, recipient race, early dialysis, and rejection within six mos. had small but statistically significant effects on median GS. However, the possible contribution of these effects over the range was small (<10%) compared to the reduction in GS associated with SCr rise. Conclusion: Rises in SCr are associated with predictable decrements in median GS. This information can be used in the design of secondary intervention trials, to estimate likely rates of graft failure endpoints, for a given rise in SCr. In addition, the decrement in GS observed with SCr rises suggests that prevention of rises above a limiting value might be a useful surrogate endpoint in the study of primary prevention of chronic graft loss. (Figure)Figure

The Impact of Welfare Benefits on the Conjugal Status of Single Mothers in Canada: Estimates from a Hazard Model

This paper focuses on the determinants of the likelihood of a remarriage (marriage) for female heads with children. Using retrospective data from Statistics Canada's 1990 Family History Survey, the study attempts to identify which socioeconomic characteristics of single mothers are conducive to conjugal union formation (formal or informal). Particular attention is given to external time-varying economic covariates, so as to disentangle the impact they exert on single mothers' propensity to start living with a (new) partner. The empirical analysis is carried out using a proportional hazards model which permits the estimation of the effects of various covariates on the hazard of exiting single parenthood. The most striking result is the strong effect of provincial welfare benefits on conjugal union formation. However, the analysis reveals that single motherhood, far from representing a final state, remains a transitory situation for a majority of women.

Bayes estimates for immunological progression rates in HIV disease.

We develop Bayesian methods for calculating shrinkage estimates of immunological progression rates (for example, CD4 count decline rates) in populations of HIV-infected patients. These methods make the assumption that decline of immunological markers may be modelled as approximately linear on some suitable chosen scale. They are applicable in situations where seroconversion times are unknown and follow-up of patients is variable, with some patients having only sparse measurements of immunological markers. Fitting of models is achieved by Gibbs sampling and CD4 count data from 603 members of the Edinburgh City Hospital Cohort with at least two CD4 determinations are analysed to provide an illustration. It is found that Bayesian shrinkage estimates for CD4 slopes on the square root scale are much more effective predictors of future CD4 counts than the least squares estimates, with respect to squared error loss. Of various shrinkage estimators considered, the most effective corresponds to the simplest model, which can also be fitted using SAS. A characterization of the pattern of CD4 loss in the Edinburgh cohort is obtained (mean rate of decline on root scale-1.61 per annum, standard deviation 1.03) and the effect of various covariates (sex, age, risk category and HLA antigen type) on immunological progression is considered. It is found that homosexual men in Edinburgh and patients with HLA haplotype A1B8DR3 experience significantly faster loss of CD4.

Exposure assessment needs in studies of acute health effects

It is known that pollutants in the outdoor and indoor environments are associated with acute adverse effects on health. The acute health effects produced include a wide range, from minor biological changes to causes of illness and exacerbation of disease, to death. Valid assessment of total exposures in various microenvironments are much more meaningful in terms of the various health responses. Short and long exposure times are both important, especially as related to the locations of such exposure and activities engaged in at the time. The quantitative character of exposure-response relationships will require more extensive research on obtaining appropriate exposure information, including monitoring and validating exposures and time activities, and on further modelling. More knowledge is also needed regarding the quantitative nature of the acute health effects, combined effects of different pollutants, and on the effects of various co-variates, effect-modifiers, and confounders. Efforts should also consist of promoting acute health effects studies that have appropriate monitoring and exposure assessment.

ESTIMATED POPULATION SIZE OF THE CALIFORNIA GRAY WHALE

Abstract: The 1987‐1988 counts of gray whales passing Monterey are reanalyzed to provide a revised population size estimate. The double count data are modeled using iterative logistic regression to allow for the effects of various covariates on probability of detection, and a correction factor is introduced for night rate of travel. The revised absolute population size estimate is 20,869 animals, with CV = 4.37% and 95% confidence interval (19,200, 22,700). In addition the series of relative population size estimates from 1967‐1968 to 1987‐1988 is scaled to pass through this estimate and modeled to provide variance estimates from interannual variation in population size estimates. This method yields an alternative population size estimate for 1987‐1988 of 21,296 animals, with CV = 6.05% and 95% confidence interval (18,900, 24,000). The average annual rate of increase between 1967‐1968 and 1987‐1988 was estimated to be 3.29% with standard error 0.44%.

Factors affecting survival of hemodialysis patients utilizing urea kinetic modeling. A critical appraisal of shortening dialysis times.

The objective of this study was to analyze risk factors affecting mortality rates (MR) in hemodialysis patients undergoing shortened dialysis time who were regularly kinetically modeled. Over a 14-month period, 180 in-center hemodialysis patients, 54% male, 46% female, 57% Black, 39% Caucasian, and 4% Hispanic, treated with rapid high efficiency dialysis (RHED = 2-3 h, 3 times/week) and conventional dialysis (3-4 h, 3 times/week) were studied. Median patient age was 56.7 years (16-84 years) and dialysis care ranged from 6 months to 18 years (mean +/- SD = 4.0 +/- 4.2 years). The patients underwent monthly urea kinetic modeling. The dialysis prescription was based upon normalizing Kt/V between 0.8 and 1.2 and the protein catabolic rate (PCRn) between 0.9 and 1.1. Thirty-three percent of the patients received recombinant human erythropoietin (r-HuEPO). The effects of various covariates, including primary diagnosis, post/predialysis BUN ratios, creatinine, albumin, calcium, phosphate, cholesterol, hemoglobin, r-HuEPO, Kt/V, and PCRn were analyzed using analysis of variance, chi 2 and linear discriminant function (DF) statistical methods. Several significant factors emerged as influencing outcome. The DF analysis produced a highly statistically significant (p < 0.0001) model to predict mortality based upon certain laboratory and dialysis parameters. Further, the linear DF correctly predicted mortality rate in 86% of cases. The results of the analysis revealed an overall mortality rate of 15.6%; hospitalization rates (HR) were 1.4 +/- 1.8 times/year. Length of dialysis time, i.e., dialysis times between 2 and 4 h, when adjusted for Kt/V has no correlation with MR or HR. Variables associated with survival were higher post/predialysis BUN ratios, normal Kt/V (0.8-1.2), normal albumin levels (> 3.5 g/dl), higher postdialysis BUN, creatinine, and cholesterol levels, and use of r-HuEPO. The use of r-HuEPO when analyzed by DF significantly improved MR, 8.3% as opposed to 19.2%. It is concluded that urea kinetic modeling permits shortening dialysis times without affecting mortality or hospitalization rates, and that low postdialysis BUN, post/predialysis BUN ratios, creatinine, and albumin values are correlated with a lower chance of survival.

Life insurance for insulin-dependent diabetics

Abstract This paper presents a study of the mortality of insulin-dependent diabetics diagnosed before age 31. The analysis includes the effect of various covariates on the mortality and on the risk of developing diabetic nephropathy, a serious renal complication associated with diabetes. The results show that it is the risk of developing nephropathy combined with very high mortality rates of patients with nephropathy which are the main reasons for the excess mortality usually experienced among insulin-dependent diabetics. The results are used to provide examples of the cost of individual life and group life insurance for diabetics who, at the time of issue of insurance, show no sign of diabetic nephropathy.

Covariance Analysis of Heart Transplant Survival Data

Abstract This paper presents a number of analyses to assess the effects of various covariates on the survival of patients in the Stanford Heart Transplantation Program. The data have been updated from previously published versions and include some additional covariates, such as measures of tissue typing. The methods used allow for simultaneous investigation of several covariates and provide estimates of the relative risk of transplantation as well as significance tests.