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At least 109 records · Page 6Linked to original sources
PubMed2006

Intestinal ischaemia following cardiac surgery: a multivariate risk model.

OBJECTIVE: Intestinal ischaemia following cardiac surgery is a serious complication, which carries a high mortality rate. Several studies have examined pre-operative and intra-operative risk factors. We aimed to develop a multivariate risk model to identify those patients at highest risk of intestinal ischaemia. METHODS: Data was prospectively collected for 10,976 consecutive cardiac surgery patients from our institution between April 1997 and March 2004. Fifty (0.5%) patients developed post-operative intestinal ischaemia. A forward stepwise multivariate logistic regression analysis was undertaken to identify predictors of developing intestinal ischaemia. Intra-operative and post-operative variables were censored at the time of onset of intestinal ischaemia. RESULTS: The predictors of post-operative intestinal ischaemia were: post-op inotrope and dialysis support (OR 6.7; p < 0.001), post-op ventilation >48 h (OR 5.1; p < 0.001), age at operation (OR 1.06 [for each additional year]; p < 0.001), post-op atrial fibrillation (OR 2.3; p = 0.014) and blood loss in intensive care unit (ICU) >700 ml (OR 2.0; p = 0.037). The predictive ability of this model was very good with an area under the receiver operating characteristic curve of 0.93. In-hospital mortality for the patients who developed intestinal ischaemia was 94% (47/50) compared to 3.6% (390/10,926) for the other patients (p < 0.001). CONCLUSIONS: Although the incidence of intestinal ischaemia following cardiac surgery is low, the prognosis for these patients is very poor. We have identified several risk factors, and developed a multivariate prediction tool, which may be useful in identifying patients at high-risk of developing intestinal ischaemia.

Acute Disease↗
PubMed1998

Goodness-of-fit tests for the additive risk model with (p > 2)-dimensional time-invariant covariates.

This paper presents methods for checking the goodness-of-fit of the additive risk model with p(> 2)-dimensional time-invariant covariates. The procedures are an extension of Kim and Lee (1996) who developed a test to assess the additive risk assumption for two-sample censored data. We apply the proposed tests to survival data from South Wales nikel refinery workers. Simulation studies are carried out to investigate the performance of the proposed tests for practical sample sizes.

Biometry↗
PubMed1997

Complications from arteriovenous malformation radiosurgery: multivariate analysis and risk modeling.

PURPOSE/OBJECTIVE: To assess the relationships of radiosurgery treatment parameters to the development of complications from radiosurgery for arteriovenous malformations (AVM). METHODS AND MATERIALS: We evaluated follow-up imaging and clinical data in 307 AVM patients who received gamma knife radiosurgery at the University of Pittsburgh between 1987 and 1993. All patients had regular clinical or imaging follow up for a minimum of 2 years (range: 24-96 months, median = 44 months). RESULTS: Post-radiosurgical imaging (PRI) changes developed in 30.5% of patients with regular follow-up magnetic resonance imaging, and were symptomatic in 10.7% of all patients at 7 years. PRI changes resolved within 3 years developed significantly less often (p = 0.0274) in patients with symptoms (52.8%) compared to asymptomatic patients (94.8%). The 7-year actuarial rate for developing persistent symptomatic PRI changes was 5.05%. Multivariate logistic regression modeling found that the 12 Gy volume was the only independent variable that correlated significantly with PRI changes (p < 0.0001) while symptomatic PRI changes were correlated with both 12 Gy volume (p = 0.0013) and AVM location (p = 0.0066). CONCLUSION: Complications from AVM radiosurgery can be predicted with a statistical model relating the risks of developing symptomatic post-radiosurgical imaging changes to 12 Gy treatment volume and location.

Follow-Up Studies↗
PubMed2003

Application of the high risk model of threat perception to medical illness and service utilization in a family practice.

This study was designed to test the High Risk Model of Threat Perception in a family practice population. Predisposing, triggering, and buffering factors were assessed in 165 patients using psychological inventories. The relationship between these factors and self-reported symptoms, diagnosed chronic problems, and utilization was assessed. Negative affect and number and intensity of life events increased the risk for chronic illness and reported symptoms, while social support and approach style of coping decreased the apparent risk. The numbers of encounters and telephone calls to the office, obtained from the office database, were statistically correlated with negative affect and inversely with social support. The regression analysis predicted 27% of the variance in reported symptoms with negative affect, life events, and avoidance coping as significant predictors. Only 8% and 16% of the variance of telephone calls and office visits, respectively, could be predicted with a similar regression model. These results emphasize the importance of psychosocial factors in medical illness. Routine assessment of psychosocial risk factors in family practice patients is suggested.

Adaptation, Psychological↗
PubMed2003

Goodness-of-fit methods for additive-risk models in tumorigenicity experiments.

In tumorigenicity experiments, a complication is that the time to event is generally not observed, so that the time to tumor is subject to interval censoring. One of the goals in these studies is to properly model the effect of dose on risk. Thus, it is important to have goodness of fit procedures available for assessing the model fit. While several estimation procedures have been developed for current-status data, relatively little work has been done on model-checking techniques. In this article, we propose numerical and graphical methods for the analysis of current-status data using the additive-risk model, primarily focusing on the situation where the monitoring times are dependent. The finite-sample properties of the proposed methodology are examined through numerical studies. The methods are then illustrated with data from a tumorigenicity experiment.

Animals↗
PubMed1989

Risk modelling: which models to choose?

Using as examples excess lung cancer mortality in coke oven workers and lung tumor induction in rats by inhalation of diesel engine emissions or cadmium chloride aerosol, the maximum likelihood estimate and the upper limit of risk were determined using a set of conventional risk models. The additional safety offered by going to the upper limit of the 95% confidence interval when deriving a unit risk value was found to be less than a factor of 5 in all but one case, and usually much less than 2. It is concluded that the selection of an adequate model is the most critical step in risk assessment, and that an additional safety factor may be required to allow for a better protection of the public in case models other than the most conservative ones come into use.

Animals↗
PubMed2006

The effects of exercise on haemodynamic function in relation to the familial hypertension risk model.

Offspring hypertensives are characterized by a hyperactive sympathetic nervous system and other early cardiovascular abnormalities that increase the risk of developing hypertension. A physically active lifestyle is associated with a lower risk of hypertension, although the mechanisms are incompletely understood and likely to be multifactorial. One aspect that has received little attention is the interaction of exercise with familial hypertension risk. The present review examines the effects of exercise on haemodynamic function in relation to the familial hypertension risk model. Paradoxically, exercise may be viewed as potent stressor to the cardiovascular system, although recent studies are beginning to show that cardiovascular adaptations, primarily mediated by changes in sympatho-vagal balance, following both acute and chronic exercise may be particularly important for individuals with familial risk of hypertension. Future studies that focus on inflammatory, metabolic, and genetic pathways may uncover further beneficial effects of exercise in relation to familial risk.

Adaptation, Physiological↗
PubMed1991

Risk models for rebleeding and postoperative mortality in bleeding gastric ulcer.

In order to better define management policies we attempted to construct risk models for rebleeding on initial conservative management and mortality after emergency surgery for failure of medical therapy in 387 patients with bleeding gastric ulcer. Several different models were constructed using logistic regression analysis with validation by the 'leaving-one-out' method. However, despite large patient numbers, modelling in this way is difficult because of inherent wide variation between patients. Suitable models for rebleeding were regarded as rather unsatisfactory, for although overall accuracy was 86%, sensitivity was only 54%. More promising was a model for mortality after emergency surgery which had an accuracy of 93% and a sensitivity of 80%. Such mortality models incorporating age, history of previous malignant disease or dyspepsia, the presence or absence of ascites and total transfusion requirements may well prove to be of value in surgical practice. This paper seeks to examine the process of modelling rebleeding and mortality and of interpreting the models produced.

Aged↗
PubMed2000

High risk model of threat perception in chronic pain patients: implications for primary care and chronic pain programs.

This study investigated the High Risk Model of Threat Perception (HRMTP) in middle-aged, urban chronic pain patients who had been referred to a secondary pain clinic after failing to respond to standard medical management. Relationships among absorption, social desirability (SD), and negative (e.g., depressive or anxious) affect were studied in 24 male and 73 female patients, (age range 22-88 years). Subjects completed the Tellegen Absorption Scale, the Marlowe-Crowne Social Desirability Scale, the Beck Depression Inventory--Second Edition, and the Beck Anxiety Inventory. The sample was significantly higher in SD and lower in absorption than normative groups. High SD patients endorsed significantly fewer items related to depression than those with low SD, but reported anxious ideation at about the same rate. These findings lend credence to the concept of chronic pain as a transduction of depressive, but not anxious, affect into somatic symptoms.

Adult↗
PubMed2006

Evaluation of the meningitis epidemics risk model in Africa.

Meningitis epidemics have a strong environmental component in Africa with the most severe epidemics occurring in the Sahelian region known as the Meningitis Belt. The objective of this study is to evaluate an ecological model based on absolute humidity and land cover type to predict the location of these epidemics. The risk model is evaluated prospectively based on epidemics occurring in Africa from January 2000 to April 2004. Seventy-one epidemics occurred during this time period affecting 22% of continental African districts. The model predicted their location with a sensitivity of 88%. The evaluation also suggests that epidemics may be extending south of the Sahel, which is consistent with environmental changes in the region. This model could be used to select priority areas for the introduction of the newly developed conjugate meningococcal vaccines. Further studies are needed to enhance our understanding of the complex relationship between meningitis epidemics and the environment.

Africa↗
PubMed2005

Combining information from multiple data sources to create multivariable risk models: illustration and preliminary assessment of a new method.

A common practice of metanalysis is combining the results of numerous studies on the effects of a risk factor on a disease outcome. If several of these composite relative risks are estimated from the medical literature for a specific disease, they cannot be combined in a multivariate risk model, as is often done in individual studies, because methods are not available to overcome the issues of risk factor colinearity and heterogeneity of the different cohorts. We propose a solution to these problems for general linear regression of continuous outcomes using a simple example of combining two independent variables from two sources in estimating a joint outcome. We demonstrate that when explicitly modifying the underlying data characteristics (correlation coefficients, standard deviations, and univariate betas) over a wide range, the predicted outcomes remain reasonable estimates of empirically derived outcomes (gold standard). This method shows the most promise in situations where the primary interest is in generating predicted values as when identifying a high-risk group of individuals. The resulting partial regression coefficients are less robust than the predicted values.

Journal Article↗
PubMedDate not supplied

Risk models for predicting chemotherapy-induced neutropenia.

Neutropenia and its complications, including febrile neutropenia, are major dose-limiting toxicities of systemic cancer chemotherapy. A number of studies have attempted to identify risk factors for neutropenia and its consequences to develop predictive models capable of identifying patients at greater risk for such complications and to guide more effective and cost-effective applications of the colony-stimulating factors. A systematic review of the literature showed that age, performance status, nutritional status, chemotherapy dose intensity, and low baseline blood cell counts were associated with the risk of severe and febrile neutropenia or reduced chemotherapy dose intensity in multivariate analysis in two or more studies. Similarly, age, diagnosis of leukemia or lymphoma, high temperature or low blood pressure at admission, and i.v. site infection along with low blood cell counts and organ dysfunction were associated with serious medical complications of febrile neutropenia, including bacteremia and death. The available risk model studies, however, had several limitations, including retrospective analyses of small study populations lacking independent validation, frequent missing values, and differences in the predictive factors considered. To overcome the limitations of previous studies, efforts are under way to develop and validate risk models based on large prospective studies in representative populations of patients receiving systemic chemotherapy.

Antineoplastic Agents↗
PubMed1996

Imputation for exposure histories with gaps, under an excess relative risk model.

In reconstructing exposure histories needed to calculate cumulative exposures, gaps often occur. Our investigation was motivated by case-control studies of residential radon exposure and lung cancer, where half or more of the targeted homes may not be measurable. Investigators have adopted various schemes for imputing exposures for such gaps. We first undertook simulations to assess the performance of five such methods under an excess relative risk model, in the presence of random missingness and under assumed independence among the true exposure levels for different epochs of exposure (houses). Assuming no other source of measurement error, one of the methods performed without bias and with coverage of nominally 95% confidence intervals that was close to 95%. This method assigns to the missing residences the arithmetic mean across all measured control residences. We show that its good properties can be explained by the fact that this approach produces approximate "Berkson errors." To take advantage of predictive information that might exist about the missing epochs of exposure, one might prefer to carry out the imputations within strata. In further simulations, we asked whether the method would still perform well if imputations were carried out within many strata. It does, and much of the lost statistical power/precision can be recovered if the stratification system is moderately predictive of the missing exposures. Thus, observed control mean imputation provides a way to impute missing exposures without corrupting the study's validity; and stratifying the imputations can enhance precision. The technique is applicable in other settings where exposure histories contain gaps.

Environmental Exposure↗
PubMed2004

The bystander effect model of Brenner and Sachs fitted to lung cancer data in 11 cohorts of underground miners, and equivalence of fit of a linear relative risk model with adjustment for attained age and age at exposure.

Bystander effects following exposure to alpha-particles have been observed in many experimental systems, and imply that linearly extrapolating low dose risks from high dose data might materially underestimate risk. Brenner and Sachs (2002 Int. J. Radiat. Biol. 78 593-604; 2003 Health Phys. 85 103-8) have recently proposed a model of the bystander effect which they use to explain the inverse dose rate effect observed for lung cancer in underground miners exposed to radon daughters. In this paper we fit the model of the bystander effect proposed by Brenner and Sachs to 11 cohorts of underground miners, taking account of the covariance structure of the data and the period of latency between the development of the first pre-malignant cell and clinically overt cancer. We also fitted a simple linear relative risk model, with adjustment for age at exposure and attained age. The methods that we use for fitting both models are different from those used by Brenner and Sachs, in particular taking account of the covariance structure, which they did not, and omitting certain unjustifiable adjustments to the miner data. The fit of the original model of Brenner and Sachs (with 0 y period of latency) is generally poor, although it is much improved by assuming a 5 or 6 y period of latency from the first appearance of a pre-malignant cell to cancer. The fit of this latter model is equivalent to that of a linear relative risk model with adjustment for age at exposure and attained age. In particular, both models are capable of describing the observed inverse dose rate effect in this data set.

Air Pollutants, Radioactive↗
PubMed2001

Early mortality and morbidity of bilateral versus single internal thoracic artery revascularization: propensity and risk modeling.

OBJECTIVES: We examined whether bilateral internal thoracic artery (BITA) revascularization is associated with any increased in-hospital mortality and complications compared with single internal thoracic artery (SITA) revascularization. BACKGROUND: Despite proven long-term benefits, BITA revascularization has been slow to be adopted because of fear of increased early morbidity. METHODS: We evaluated 1,697 consecutive patients undergoing BITA (n = 867) or SITA (n = 830) revascularization. We used propensity score analyses and adjusted risk models to address differences between arms. RESULTS: There were 20 (2.3%) deaths in the BITA group versus 26 (3.1%) in the SITA group (odds ratio 0.73, p = 0.30). Propensity analysis identified several parameters that affected the decision to use BITA. Adjusting for propensity score and all potential risk factors, the odds ratio for death with BITA versus SITA was practically 1. Bilateral internal thoracic artery revascularization did not increase the number of in-hospital complications with the possible exception of deep sternal wound infections (11 [1.3%] vs. 3 [0.4%], p = 0.057). In multivariate modeling BITA increased the risk of deep sternal wound infections only in emergent cases and in older patients; the excess risk was negligible among 1,206 patients (71.1% of total) who did not have emergent revascularization and were < or =70 years old (risk difference 0.3%, p = 0.74). There was no difference in length of stay after adjustment for propensity factors (mean 11.3 vs. 11.7 days, p = 0.66). CONCLUSIONS: Bilateral internal thoracic artery revascularization grafting confers no increased risk for early death and does not prolong hospital stay. The small increase in the risk of deep sternal wound infections does not affect the majority of patients.

Aged↗
PubMed2004

Two simulation methods for constructing confidence bands under the additive risk model.

With right-censored failure time data, we propose procedures to construct simultaneous confidence bands for the survival curve of a given subject under the additive risk model. The distribution of the subject-specific cumulative hazard function can be approximated with a zero-mean Gaussian process, which can be generated through simulation methods. We propose two different simulation schemes to obtain the distribution of the supremum of the cumulative hazard process over the entire time range. The two simulation approaches are asymptotically equivalent, whereas the numerical forms are different. We construct two types of confidence bands, namely the equal precision band and the Hall-Wellner type band, through choosing suitable weight functions. Monte Carlo simulation studies show that both of the proposed confidence bands are appropriate for finite sample sizes. We illustrate the new proposal with a real example.

Computer Simulation↗
PubMed1987

Model risk analysis of nitrosatable compounds in the diet as precursors of potential endogenous carcinogens.

The potential health risk posed by the endogenous formation of N-nitroso compounds (NOC) from nitrosation of dietary ureas, guanidines, amides, amino acids and amines (primary, secondary and aromatic) was estimated according to the model: Risk = [daily intake of precursor] X [gastric concentration of nitrite]n X [nitrosatability rate constant] X [carcinogenicity of derivative]. The daily intakes of these compound classes span five orders of magnitude (100 g/day amides, top; 1-10 mg/day secondary amines, ureas, bottom); the nitrosation rate constants span seven orders of magnitude (aryl amines, ureas, top; amides, secondary amines, bottom); and the carcinogenicity estimates span a 10,000-fold range from 'very strong' to 'virtually noncarcinogenic'. The resulting risk estimates likewise span an enormous range (nine orders of magnitude): dietary ureas and aromatic amines combined with high nitrite concentration could pose as great a risk as the intake of preformed N-nitrosodimethylamine in the diet. In contrast, the risk posed by the in-vivo nitrosation of primary and secondary amines is probably negligible. The risk contributed by amides (including protein), guanidines and primary amino acids is intermediate between these two extremes.

Amines↗
PubMed2001

[Cox proportional risk model analysis on the affecting factors of liver transplantation].

OBJECTIVE: To analyze the relative factors affecting the survival time of liver transplantation and identify the main factors for the purpose of supply the reference evidence to the clinic. METHODS: The clinical data on preoperative condition, interoperation and liver function in 116 out of 128 recipients were quantified by the cox proportional risk model after liver transplantation. Their variables were calculated and analyzed by cox regression under the SAS 6.12 software. RESULTS: Z14 (FFP) was obvious at alpha = 0.05. After deleting the non-obvious factors from the model, regression coefficient, standard errors, wald, P and RR were 0.065, 0.024, 7.493, 0.006 and 1.067 respectively. There was no difference of survival time between living liver transplantation and cadaver liver transplantation. The relative dangerous degree in cadaver liver transplantation was 0.340 as much as that in living liver transplantation. CONCLUSIONS: Living liver transplantation shortens the waiting time of liver transplantation and alleviates patient's suffering. It suits for children and adult and supports a selective liver transplantation.

Adolescent↗