Biomedical subjects

C Quantin

Publications and source records attributed to C Quantin.

At least 37 records · Page 2Linked to original sources

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.

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.

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↗

PubMed1998

How to ensure data security of an epidemiological follow-up: quality assessment of an anonymous record linkage procedure.

A computerised record hash coding and linkage procedure is proposed to allow the chaining of medical information within the framework of epidemiological follow-up. Before their extraction, files are rendered anonymous using a one-way hash coding based on the standard hash algorithm (SHA) function, in order to respect the legislation on data privacy and security. To avoid dictionary attacks. two keys have been added to SHA coding. Once rendered anonymous, the linkage of patient information can be accomplished by means of a statistical model, taking into account several identification variables. Quality assessment of this anonymous record linkage procedure shows a specificity of 100% and a sensitivity of 95%.

Algorithms↗

PubMed1998

Security aspects of medical file regrouping for the epidemiological follow-up.

To carry out epidemiological studies at a regional level, one may need to link information collected by medical doctors working either in hospitals or in private offices or laboratories. The first problem is to respect the European legislation on nominal data processing, which does not allow the linkage of nominal files. As a consequence, we have developed an anonymous record linkage procedure, which ensures an irreversible transformation of identity and allows the linkage of rendered anonymous files. The second problem is to ensure data security during the transmission and we discuss the advantages of different methods of communication such as the norms X400 and Internet protocols.

Computer Communication Networks↗

PubMed1998

Automatic record hash coding and linkage for epidemiological follow-up data confidentiality.

A protocol is proposed to allow linkage of anonymous medical information within the framework of epidemiological follow-up studies. The protocol is composed of two steps; the first concerns the irreversible transformation of identification data, using a one-way hash function which is used after spelling processing. To avoid dictionary attacks, two large random files of keys, called pads, are introduced. The second step consists in the linkage of files rendered anonymous. The weight given to each linkage field is estimated by a mixture model, the likelihood of which being maximized with the Expectation and Maximization (EM) algorithm. The performance of this method has been assessed by comparing record linkage, based on exclusive use of the automatic procedure, with a manual linkage, obtained by the Burgundy Registry of Digestive Cancers. The result of the linkage of a file of 2,847 cancers with a file of 388,614 hospitalization stays in the Dijon university hospital showed a sensitivity of 97% and a specificity of 93%.

Algorithms↗

PubMed1997

A hospital-based and a population-based stroke registry yield different results: the experience in Dijon, France.

BACKGROUND AND PURPOSE: The aim of this study was to demonstrate the different results obtained from a population-based and a hospital-based stroke study in the same city. METHODS: Between January 1 and December 31, 1993, we collected information on all of the first strokes in the population of the city of Dijon, in conjunction with the Dijon Stroke Registry, collecting the first-ever strokes from patients living in Dijon as well as on all the first strokes in residents and nonresidents of Dijon who were treated at Dijon University Hospital. Demographic details, medical history, vascular risk factors, stroke subtype, as diagnosed by CT scan, and mortality rates were compared between the strokes observed in the population of the city of Dijon among residents as well as nonresidents in Dijon who were treated at Dijon University Hospital. RESULTS: We collected information on 210 strokes observed in the population of Dijon city, 171 Dijon residents and 395 non-Dijon city residents hospitalized at the University Hospital of Dijon. These three groups were quite different. The residents of Dijon treated for stroke at the University Hospital were younger and their incidence of cerebral hemorrhage, cardiac arrhythmia, ischemic heart disease and case fatality rate were higher than those from the Dijon Stroke Registry. CONCLUSIONS: Type of stroke data bank is very important in order to describe cerebrovascular disease. Hospital-based studies tend to include more severe strokes, those occurring in a younger population, and those having a higher mortality. Population-based studies, on the other hand, give a somewhat different picture of stroke.

Age Distribution↗

PubMed1997

A computerized record hash coding and linkage procedure to warrant epidemiological follow-up data security.

A computerized record hash coding and linkage procedure is proposed to allow the chaining of medical information within the framework of epidemiological follow-up. Before their extraction, files are rendered anonymous using a one-way hash coding based on the SHA function, in order to respect the legislation on data privacy and security. To avoid dictionary attacks, two keys have been added to SHA coding. Once rendered anonymous, the linkage of patient information can be accomplished by the means of a statistical model, taking into account several identification variables.

Confidentiality↗

PubMed1997

[Modelling of length of stay and costs in 2 homogeneous groups of hematological and pneumological patients: clinical characterization of patients with long-stay and high costs].

After the implementation of the Medicare Prospective Payment System (PPS) in the USA, many European countries like France have introduced DRGs to curb hospital overspending. However, there has been some reluctance from hospital actors, especially because of the heterogeneous nature of DRG's. To analyse this situation, we propose a method based on distribution modelization of length of stays and costs within DRGs. For each DRG, the model is based on a mixture of Poisson and Weibull distributions identified as subgroups. The subgroups are characterized by their means and their proportions which are estimated by maximization of data likelihood. For a particular DRG, the proportion of long stay or high-cost patients can be explained by the introduction of clinical variables in the model. First the model was applied to the DRG "leukemia and lymphoma" (HCFA V.3), using 133 discharge abstract files from the Dijon public teaching hospital which were classified into this DRG in 1993. Among the studies parameters only acute leukemia, neutropenia < 500 PNN/mm3, high dose aplastic chemotherapy, central venous catheterization, parenteral nutrition, use of protected or laminar air flow room, septicemia, large spectrum intravenous antibiotherapy, and blood transfusion had a significant influence on the distribution of the patients in the long stay or costly subgroup. Second, for DRG "chronic bronchopneumopathies" (n = 220) the significant parameters were mechanical ventilation, antibiotherapy, post hospitalization medicalized care.

Adolescent↗

PubMed1996

A regression survival model for testing the proportional hazards hypothesis.

A semi-parametric generalization of the proportional hazards regression model is defined, whereby the hazard functions can cross for different values of the covariates. In the two-sample comparison, it includes in particular the case of two Weibull distributions differing in scale and shape parameters. A global test of the proportional hazards assumption is proposed against such defined alternatives. Its power in the two-sample case is compared to that of previously described tests by using simulation experiments. Survival data of patients with breast carcinoma, including several prognostic factors, are presented as an illustration.

Antineoplastic Agents↗