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71.
One important goal in multi-state modelling is to explore information about conditional transition-type-specific hazard rate functions by estimating influencing effects of explanatory variables. This may be performed using single transition-type-specific models if these covariate effects are assumed to be different across transition-types. To investigate whether this assumption holds or whether one of the effects is equal across several transition-types (cross-transition-type effect), a combined model has to be applied, for instance with the use of a stratified partial likelihood formulation. Here, prior knowledge about the underlying covariate effect mechanisms is often sparse, especially about ineffectivenesses of transition-type-specific or cross-transition-type effects. As a consequence, data-driven variable selection is an important task: a large number of estimable effects has to be taken into account if joint modelling of all transition-types is performed. A related but subsequent task is model choice: is an effect satisfactory estimated assuming linearity, or is the true underlying nature strongly deviating from linearity? This article introduces component-wise Functional Gradient Descent Boosting (short boosting) for multi-state models, an approach performing unsupervised variable selection and model choice simultaneously within a single estimation run. We demonstrate that features and advantages in the application of boosting introduced and illustrated in classical regression scenarios remain present in the transfer to multi-state models. As a consequence, boosting provides an effective means to answer questions about ineffectiveness and non-linearity of single transition-type-specific or cross-transition-type effects. 相似文献
72.
Missing covariate values is a common problem in survival analysis. In this paper we propose a novel method for the Cox regression model that is close to maximum likelihood but avoids the use of the EM-algorithm. It exploits that the observed hazard function is multiplicative in the baseline hazard function with the idea being to profile out this function before carrying out the estimation of the parameter of interest. In this step one uses a Breslow type estimator to estimate the cumulative baseline hazard function. We focus on the situation where the observed covariates are categorical which allows us to calculate estimators without having to assume anything about the distribution of the covariates. We show that the proposed estimator is consistent and asymptotically normal, and derive a consistent estimator of the variance–covariance matrix that does not involve any choice of a perturbation parameter. Moderate sample size performance of the estimators is investigated via simulation and by application to a real data example. 相似文献
73.
A Proportional Hazards Regression Model for the Subdistribution with Covariates‐adjusted Censoring Weight for Competing Risks Data 下载免费PDF全文
Peng He Frank Eriksson Thomas H. Scheike Mei‐Jie Zhang 《Scandinavian Journal of Statistics》2016,43(1):103-122
With competing risks data, one often needs to assess the treatment and covariate effects on the cumulative incidence function. Fine and Gray proposed a proportional hazards regression model for the subdistribution of a competing risk with the assumption that the censoring distribution and the covariates are independent. Covariate‐dependent censoring sometimes occurs in medical studies. In this paper, we study the proportional hazards regression model for the subdistribution of a competing risk with proper adjustments for covariate‐dependent censoring. We consider a covariate‐adjusted weight function by fitting the Cox model for the censoring distribution and using the predictive probability for each individual. Our simulation study shows that the covariate‐adjusted weight estimator is basically unbiased when the censoring time depends on the covariates, and the covariate‐adjusted weight approach works well for the variance estimator as well. We illustrate our methods with bone marrow transplant data from the Center for International Blood and Marrow Transplant Research. Here, cancer relapse and death in complete remission are two competing risks. 相似文献
74.
Staying strong: gender ideologies among African-American adolescents and the implications for HIV/STI prevention 总被引:1,自引:0,他引:1
Kerrigan D Andrinopoulos K Johnson R Parham P Thomas T Ellen JM 《Journal of sex research》2007,44(2):172-180
This paper explores adolescents' definitions of what it means to be a man and a woman, the psycho-social context surrounding the formation of gender ideologies and their relationship to HIV/STI prevention. Semi-structured, in-depth interviews were conducted with fifty African-American adolescents living in Baltimore, Maryland. Female gender ideologies included economic independence, emotional strength and caretaking. Male gender ideologies emphasized financial responsibility, toughness and sexual prowess. Findings suggest that stronger adherence to male gender ideologies related to toughness and sexual prowess is influenced by male participants' perceived inability to fulfill their primary gender role as economic providers and the importance of gaining approval from male peers in the absence of adult male role models. Stronger adherence to female gender ideologies related to emotional strength and caretaking may be linked to a heightened desire for male intimacy and tolerance of male sexual risk behavior. Implications of the gender ideologies documented and their commonalities are discussed in terms of HIV/STI prevention. 相似文献
75.
76.
LaBrie RA LaPlante DA Nelson SE Schumann A Shaffer HJ 《Journal of gambling studies / co-sponsored by the National Council on Problem Gambling and Institute for the Study of Gambling and Commercial Gaming》2007,23(3):347-362
Internet gambling is growing rapidly, as is concern about its possible effect on the public’s health. This paper reports the
results of the first prospective longitudinal study of actual Internet sports gambling behavior during eight study months.
Data include recorded fixed-odds bets on the outcome of sporting contests and live-action bets on the outcome of events within
contests for 40,499 Internet sports gambling service subscribers who enrolled during February 2005. We tracked the following
primary gambling behaviors: daily totals of the number of bets made, money bet, and money won. We transformed these variables
into measures of gambling involvement. We analyzed behavior for both fixed-odds and live-action bets. The median betting behavior
of the 39,719 fixed-odds bettors was to place 2.5 bets of €4 (approximately $5.3 US) every fourth day during the median 4 months
from first to last bet. This typical pattern incurred a loss of 29% of the amount wagered. The median betting behavior of
the 24,794 live-action bettors was to place 2.8 wagers of €4 every fourth day during the median duration of 6 weeks at a loss
of 18% of the amount wagered. We also examined the behavior of empirically determined groups of heavily involved bettors whose
activity exceeded that of 99% of the sample. 相似文献
77.
Campbell TA Auerbach SM Kiesler DJ 《Journal of American college health : J of ACH》2007,55(6):333-340
OBJECTIVE: The authors' aim was to evaluate patient-provider relationships in a college health center. PARTICIPANTS: Eighty student patients and their health-care providers. METHODS: Patients completed a measure of perceived health competence before a consultation and measures of provider participatory behavior and interpersonal behavior before and after the consultation. They evaluated their satisfaction with care and compliance after the consultation and again 2 weeks later. Providers completed measures of their participatory behavior and patients' interpersonal behavior after the consultation. RESULTS: Patients preferred to be well informed and to have their preferences taken into account, and generally felt competent at managing their own health affairs. They indicated they obtained the high level of participation they desired. Patients desired and actually experienced friendly and submissive providers. Degree of match between patients' desired and actual level of involvement in their care was associated with greater satisfaction. A greater match between the extent to which they desired the provider to be affiliative and the provider's actual affiliative behavior was associated with more satisfaction. No variables were predictive of patient compliance. CONCLUSION: The authors discuss results in terms of the influence of situational factors characteristic of a college health center. 相似文献
78.
Howard DE Griffin M Boekeloo B Lake K Bellows D 《Journal of American college health : J of ACH》2007,56(3):247-254
OBJECTIVE: In this qualitative study, the authors examined how students attempt to minimize harm to themselves and others when drinking. PARTICIPANTS: The authors recruited freshmen at a large, mid-Atlantic US public university during the fall semester of 2005 to participate in 8 focus groups. METHODS: The moderator's guide was developed through an iterative process that included input from experts and pilot testing. The researchers audiotaped focus group conversations, transcribed them, and subjected them to an interrater reliability check. Analysis was based on the framework of Information-Motivation-Behavioral Skills Model and a phenomenological approach. RESULTS: College students have a repertoire of coping strategies they use in an attempt to safeguard themselves and their friends from harm when drinking. Strategies encompass planning a safe context for drinking, using safety measures to minimize harm when drinking, and taking care of someone who has consumed too much alcohol. CONCLUSIONS: A harm-reduction focus that acknowledges and builds on existing protective strategies may be a promising avenue for alcohol interventions. 相似文献
79.
Unplanned sexual activity as a consequence of alcohol use: a prospective study of risk perceptions and alcohol use among college freshmen 总被引:1,自引:0,他引:1
OBJECTIVE: The authors' goal was to show how risk perceptions regarding unplanned sexual activity following alcohol use are prospectively related to subsequent alcohol consumption. PARTICIPANTS: Undergraduate students (N = 380) completed questionnaires at 2 time points during their freshman year. METHODS: In the middle of the academic year (T1), students estimated their risk of engaging in unplanned sex and reported their alcohol use during the previous term. Four months later (T2), they again reported alcohol use and indicated whether they had engaged in unplanned sex since T1. RESULTS: Students who consumed more alcohol at T1 rated their risk of unplanned sex more highly, suggesting relative accuracy. Those with higher risk perceptions consumed more alcohol at T2 (controlling for T1 use), suggesting that they maintained the high-risk behavior. Last, those who were unrealistically optimistic (ie, estimated low risk at T1 yet had unplanned sex by T2) reported greater alcohol use at T2. CONCLUSIONS: These findings highlight the role that risk perceptions regarding sexual activity may play in college students' alcohol use. 相似文献
80.
Shumway ST Kimball TG Korinek AW Arredondo R 《Journal of marital and family therapy》2007,33(2):134-148
Employee assistance professionals are expected to be proficient at intervening in organizations and creating meaningful behavioral change in interpersonal functioning. Because of their training in family systems theories and concepts, marriage and family therapists (MFTs) are well suited to serve organizations as "systems consultants." Unfortunately, the authors were unable to identify any family systems-based models for organizational intervention that have been empirically tested and supported. In this article, the authors present a family systems-based model of intervention that they developed while working in an employee assistance program (EAP). They also present research that was used to refine the model and to provide initial support for its effectiveness. 相似文献