Biomedical subjects

C Quantin

Publications and source records attributed to C Quantin.

At least 19 recordsLinked to original sources

PubMed2001

Modelling time-dependent hazard ratios in relative survival: application to colon cancer.

The Cox model is widely used in the evaluation of prognostic factors in clinical research. In population-based studies, however, which assess long-term survival of unselected populations, relative survival models are often considered more appropriate. In both approaches, the validity of proportional hazard hypothesis should be evaluated. To explore the validity of the proportional hazard assumption in a population-based study of colon cancer, to propose non-proportional hazard relative survival models and to evaluate their utility. The use of a piecewise proportional hazard relative survival model in colon cancer has shown that the effects of most clinical prognostic factors such as age, period of diagnosis and stage are non-proportional. The non-proportional hazard relative survival models developed in this article have been found to be efficient tools for better understanding the time-dependent aspect of prognostic factors.

Aged↗

PubMed2001

An approach for integrating heterogeneous information sources in a medical data warehouse.

In recent years, medical professionals are witnessing an explosive growth in data collected by various organizations and institutions. At the same time, the ongoing developments of networking technologies provide doctor with the capability to access these data across the boundaries of interconnected computers. In this paper we present a medical data warehousing methodology that aims to use data semantics to regroup and merge patients' medical data from different health information systems, which may be autonomous and heterogeneous. The proposed solution takes into account European laws concerning the security and anonymity of personal data.

Database Management Systems↗

PubMed2001

Quality assessment of cervical screening: a population-based case-control study in the C te-D'Or region, France.

Our objectives were to evaluate the effectiveness of cervical cancer screening outside organized programs in the prevention of cervical carcinoma in situ (CIS) and to enhance the way in which case control studies avoid some common biases. In our case-control study, we assessed all incident, histologically verified cases of CIS registered from 1987 to 1997 in the population-based cancer registry of C te-d'Or, France (N = 104) and 208 controls randomly selected from the screened population and matched for age, date of last screening, residence, and pathology laboratory results. We considered as appropriate for controls screened women who had had at least one Papanicolaou smear in the 3 years preceding the diagnosis or similar period. Screening for controls was higher (67.8%) than for cases (41.4%; P < .001), with a relative protection against CIS of 3.09 (95% confidence interval, 1.83-5.22) and a prevented fraction in the screened population of 45% to 50%. These findings suggest a protective advantage for CIS even in the absence of organized screening. The methodologic approach has advantages as compared to previous types of case-control studies. Although further refinements still are warranted, learning about the protective effect of screening for CIS provides information that may be useful in assessing the impact of a screening policy on women actually at risk of invasive cervical cancer.

Carcinoma in Situ↗

PubMed2001

A virtual intranet and data-warehousing for healthcare co-operation.

As patient's medical data is disseminated in different health structures, developing a medical or epidemiological patient-oriented data warehouse has some specific requirements compared to intra healthcare structure data-warehousing projects. The difference is that the healthcare structures implicated in a patient-oriented data warehouse project require some considerations about the confidentiality of the patient data and of the activities of healthcare structures. Building a data-warehousing system at a regional level, for example in cancerology, requires the participation of all concerned health structures, as well as different health professionals. The heterogeneity of sources medical data of has to be taken into account for choosing between several organizational configurations of the data warehousing system. In top of data warehousing, we propose a concept of Virtual Intranet, which provides a solution to the problem of medical information security arising from heterogeneous sources.

Computer Communication Networks↗

PubMed2001

The Swiss solution for anonymously chaining patient files.

Being able to link the successive hospitalizations of a given patient for epidemiological surveys together by preserving patient anonymity requires a specific procedure. For its medical hospital statistics, Switzerland has adopted anonymous record linkage procedure, ensuring an irreversible transformation of identity and allowing the linkage of anonymous files. Concepts, algorithms and organization have been developed by the Federal Statistical Office. Algorithms are closed to those developed in Dijon University Hospital.

Algorithms↗

PubMed2001

[Using discharge abstracts as a tool to assess a regional perinatal network].

To assess the regional perinatal network of Burgundy (20 obstetrical units; 18,000 births/year), discharge abstracts are collected for all mothers and all neonates. Discharge abstracts are expanded with some additional data. According to the French law, data are rendered anonymous in each hospital before their transmission to the teaching hospital for statistical analysis. The linkage of all anonymous information concerning a patient is obtained. Moreover, this specific procedure allows the linkage of data concerning each mother and her corresponding neonate. This study shows that after an expanded data quality control, the linkage between data of the mothers and their infants is obtained in 99.8% of births.

Adult↗

PubMed2000

Anonymous statistical methods versus cryptographic methods in epidemiology.

Sensitive data are most often indirectly identifiable and so need to be rendered anonymous in order to ensure privacy. Statistical methods to provide anonymity require data perturbation and so generate data processing difficulties. Encryption methods, while preserving confidentiality, do not require data modification.

Journal Article↗

PubMed2000

[Security services: an overview of the French legislation on cryptography].

This paper deals with the main security services of data protection: integrity, authentication, nonrepudiation and confidentiality. It describes the different tools which may be used to achieve these security objectives: encryption, digital signature, access controls, integrity control, audit and certification. The French legislation concerning encryption has been recently updated in order to simplify the use of encryption techniques for personal data security. This legislation describes different authorization or reporting procedures according to the type of the request (application, equipment, import or export of encryption techniques) and the security level required.

Algorithms↗

PubMed2000

[Security of healthcare data networks used for epidemiological studies].

Record linkage, for compiling sameperson records from various source files, can improve the feasibility of epidemiological research using populationbased studies. The question is comply with the European legislation on data privacy and data security. For example, a computerized record hash coding and linkage procedure is described to link medical information within the framework of epidemiological followup. Before their extraction, files are rendered anonymous using a oneway hash coding based on the standard hash algorithm (SHA) function. Once rendered anonymous using the software ANONYMAT, the linkage of patient information can be accomplished by means of a mixture model, taking into account several identification variables. An application of this anonymous record linkage procedure was carried out in order to link medical files on cancer, from 3 hospitals of the French RhôneAlpes region. This application stresses how the use of the ANONYMAT software allows compliance with the legislation on data confidentiality without entailing problems on data availability.

Computer Communication Networks↗

PubMed2000

Anonymous statistical methods versus cryptographic methods in epidemiology.

Computer Security↗

PubMed1999

Variation over time of the effects of prognostic factors in a population-based study of colon cancer: comparison of statistical models.

The authors compare the performance of different regression models for censored survival data in modeling the impact of prognostic factors on all-cause mortality in colon cancer. The data were for 1,951 patients, who were diagnosed in 1977-1991, recorded by the Registry of Digestive Tumors of Côte d'Or, France, and followed for up to 15 years. Models include the Cox proportional hazards model and its three generalizations that allow for hazard ratio to change over time: 1) the piecewise model where hazard ratio is a step function; 2) the model with interaction between a predictor and a parametric function of time; and 3) the non-parametric regression spline model. Results illustrate the importance of accounting for non-proportionality of hazards, and some advantages of flexible non-parametric modeling of time-dependent effects. The authors provide empirical evidence for the dependence of the results of piecewise and parametric models on arbitrary a priori choices, regarding the number of time intervals and specific parametric function, which may lead to biased estimates and low statistical power. The authors demonstrate that a single, a priori selected spline model recovers a variety of patterns of changes in hazard ratio and fits better than other models, especially when the changes are non-monotonic, as in the case of cancer stages.

Aged↗

PubMed1999

Modeling of high-cost patient distribution within renal failure diagnosis related group.

Modeling by mixed-distribution was proposed in order to analyze heterogeneity of costs and length of stays within Diagnosis Related Groups (DRGs). A mixed-distribution model based on Weibull distributions was applied to 791 discharge abstracts of French DRG no. 450 (Health Care Financing Administration 3 DRG no. 316 "Renal failure") from a national database. Three subgroups of cost and length of stay were identified. Except for age, clinical criteria significantly linked with the long-stay subgroup were the same as those associated with the high-cost subgroup: acute renal failure, intensive care, infectious complications, and vascular investigations. The identification of factors associated with high costs, based on the proposed model, will allow physicians to understand more accurately how their choice of specific procedures influences hospital costs.

Costs and Cost Analysis↗

PubMed1999

High cost factors for leukaemia and lymphoma patients: a new analysis of costs within these diagnosis related groups.

STUDY OBJECTIVE: To determine high cost factors to help managers and clinicians to analyse the reasons of adverse costs and provide indications for financial negotiation. DESIGN: To locate high cost or long stay patients, the analysis was designed on the basis of a mixture of Weibull distributions. In this new model, the proportion of high cost patients was expressed according to the multinomial logistic regression, permitting the determination of high cost factors. SETTING: The 1993 French reference database, constituted in the framework of the national study of DRG costs, conducted by the French Ministry of Health. The database of discharge abstracts recorded in 1993 in the Dijon public teaching hospital. PARTICIPANTS: The analyses were based on 1352 abstracts from the French reference database and 368 from the Dijon database concerning patients, aged 18 and over, suffering from leukaemia and lymphoma. MAIN RESULTS: High cost and long stay factors were the same: number of stays, death, transfer, acute leukaemia, neutropenia, septicaemia, high dose aplastic chemotherapy, central venous catheterisation, parenteral nutrition, protected or laminar airflow room, blood transfusion, and intravenous antibiotherapy. CONCLUSIONS: Taking into account high cost predictive factors, as shown in the case of leukaemia and lymphoma patients, would help to reduce the adverse effects of a prospective payment system.

Adolescent↗

PubMed1999

Testing the proportional hazards assumption in medical survival studies--application to a population-based study of acute myeloid leukaemia.

BACKGROUND: In the analysis of survival data using the Cox proportional hazard model, it is assumed that the magnitude of mortality risk for a predictor variable remains proportional over time. The time-dependent linear model and the piece-wise proportional hazard model (two or four intervals) take into account the variation of the risk over the entire follow-up period. METHOD: The three existing models were applied to a series of 266 patients with acute myeloid leukaemia (AML), diagnosed between 1980 and 1992 and recorded by the Registry of Hematopoietic Neoplasms in Côte d'Or, France. RESULTS: A non-proportional effect of age, period of diagnosis, whether the illness was primary or secondary and French-American-British (FAB) subtype was found significant. In particular, the effect of M2 versus M4-M5 subtypes was revealed by the non-proportional analyses, although this effect was non-significant using the Cox model. CONCLUSIONS: The clinical explanation of the variation of these effects over time is discussed, for example, relating the increase over time of the positive effect of the period of diagnosis to therapeutic improvements. Confirmation of these results on an independent data set is required.

Acute Disease↗

PubMed1999

[Prognostic factors of recurrence and/or death in colorectal cancer: multistate modeling].

Analysis of survival of patients with cancer sets particular epidemiological and statistical problems, especially when one wants to take into account metastasis or local recurrences. Cox's model does not allow modeling multiple events. Wei et al. have proposed an extension of Cox's model, by formulating the marginal distributions of multivariate failure times, which allows testing covariates effects on different events. We applied these methods to data from the Registry of Digestive Tumors of Burgundy, France. Prognostic factors of recurrence are rectal location of tumor and advanced stage at diagnosis. Prognostic factors of death are male gender, age greater than 75, rectal location and advanced stages. However, relative risk of recurrence for advanced stages is significantly greater than relative risk of death (p=4.10(-3)), while tumor location has the same influence on the two events.

Aged↗

PubMed1999

Can a database be anonymous?

Computer Communication Networks↗

PubMed1999

Application of the medical data warehousing architecture EPIDWARE to epidemiological follow-up: data extraction and transformation.

In this paper, we present an application of EPIDWARE, medical data warehousing architecture, to our epidemiological follow-up project. The aim of this project is to extract and regroup information from various information systems for epidemiological studies. We give a description of the requirements of the epidemiological follow-up project such as anonymity of medical data information and data file linkage procedure. We introduce the concept of Data Warehousing Architecture. The particularities of data extraction and transformation are presented and discussed.

Computer Systems↗

PubMed1998

Does hepatitis C virus co-infection accelerate clinical and immunological evolution of HIV-infected patients?

OBJECTIVE: To study the influence of hepatitis C virus (HCV) co-infection on clinical and immunological evolution of HIV-infected patients. DESIGN: A longitudinal study of HIV-infected individuals with or without HCV infection, identified at the Infectious Diseases Department of Dijon University Hospital and enrolled in a historical cohort, was performed. METHODS: One hundred and nineteen HIV-infected people co-infected with HCV and 119 matched individuals infected with HIV alone were included in the cohort (median participation time 3 years; range, 2 months to 11.5 years). Clinical progression was defined as one or more of the following: a 30% decrease in the Karnofsky index; a 20% loss of body weight; an AIDS-defining illness (for non-AIDS patients); death (except by accident, suicide or overdose). Immunological progression was defined as a 50% decrease in the initial CD4 T-cell count (for patients with an initial count > 100 x 10(6) cells/l). Effects of HCV co-infection were evaluated using Kaplan-Meier survival analysis and significance was tested using univariate (log-rank and Peto's tests) and multivariate methods (Cox's model). RESULTS: In univariate analysis, immunological progression was not statistically different between the HCV-positive group and the HCV-negative group, whereas clinical progression was significantly faster in HCV-positive patients (P < 0.005, log-rank test). In a multivariate Cox model, clinical progression remained significantly associated with infection by HCV [hazard ratio (HR), 1.64; 95% confidence interval (CI), 1.06-2.55; P < 0.05]. Stratified multivariable analysis retained HCV as a significant prognostic factor of clinical progression (HR, 10.9; 95% CI, 1.09-109.3; P < 0.05) and immunological progression (HR, 2.31; 95% CI, 1.16-4.62; P < 0.02) for patients with an initial CD4 count above 600 x 10(6) cells/l. CONCLUSIONS: Clinical progression is more rapid in HIV-HCV co-infected patients than in HIV-seropositive patients are not infected by HCV. The prognostic value of HCV infection for both clinical and immunological progression is significant at early stages of HIV infection. These findings may argue for active management of hepatitis C infection in co-infected individuals, especially for asymptomatic patients whose CD4 count is above 600 x 10(6) cells/l, to predict and prevent accelerated progression of HCV and HIV diseases.

Adult↗