Biomedical subjects

C Quantin

Publications and source records attributed to C Quantin.

At least 37 records · Page 2Linked to original sources

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?

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 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↗

PubMed1996

Extraction and anonymity protocol of medical file.

To carry out the epidemiological study of patients suffering from a given cancer, the Department of Medical Informatics (DIM) has to link information coming from different hospitals and medical laboratories in the Burgundy region. Demands from the French department for computerized information security (Commission Nationale de l'Informatique et des Libertés: CNIL), in regard to abiding by the law of January 6, 1978, completed by the law of July 1st, 1994 on nominal data processing in the framework of medical research have to be taken into account. Notably, the CNIL advised to render anonymous patient identities before the extraction of each establishment file. This paper describes a recently implemented protocol, registered with the French department for computerized information security (Service Central de la Sécurité des Systèmes d'information : SCSSI) whose purpose is to render anonymous medical files in view of their extraction. Once rendered anonymous, these files will be exportable so as to be merged with other files and used in a framework of epidemiological studies. Therefore, this protocol uses the Standard Hash Algorithm (SHA) which allows the replacement of identities by their imprints while ensuring a minimal collision rate in order to allow a correct linkage of the different information concerning the same patient. A first evaluation of the extraction and anonymity software with regard to the purpose of an epidemiological survey is described here. In this paper, we also show how it would be possible to implement this system by means of the Internet communication network.

Computer Communication Networks↗

PubMed1995

Structural and conjunctural compensation method for hospital budgetary allocation on the basis of DRGs.

We propose here a structural and conjunctural compensation method to improve budgetary allocation which could be based on Diagnosis Related Groups. This method consists in the determination of sub-group costs within DRGs. The specification of these sub-groups is possible by introducing clinical and social parameters in the statistical model. Hospitals could then compare their sub-group proportions and analyze their differences in relation to conjunctural factors (recruitment, medical practices) and structural factors (technical team, local medical structure). This method also allows an identification of specialty hospitals (outliers) and a compensation allocation for budgeting for these hospitals.

Budgets↗

PubMed1995

A one way public key cryptosystem for the linkage of nominal files in epidemiological studies.

An encryption method is proposed for nominal files to allow their linkage while respecting confidentiality rules. In contrast to most encryption algorithms, this encryption method must be non-reversible. The method is based on congruence, like the SAN MARCO algorithm, and satisfies the two following conditions. 1) Non-reversible enciphering, which implies the possibility of collisions. 2) The collision rate must be minimized, to allow file linkage. The security of this method is, in addition, guaranteed by a key, which is destroyed after enciphering and is not given to the recipient of the coded file.

Algorithms↗

PubMed1992

A model for quality assessment in cervical cytology used as a screening test.

Although many reliability studies on cervical cytology have been carried out, measurements of sensitivity and specificity have rarely been made since biopsies are not often performed on patients with a negative smear result. This screening assessment was performed over 3 years, using a database of 230,167 smears from 177,051 women. It would seem that cervical cytology has a high specificity (over 99%) but a relatively low sensitivity (61%). Values for sensitivity (exceeding 95%) and specificity (exceeding 99%) for invasive carcinoma should be regarded as reasonably accurate as all incident cases of symptomatic cervical carcinoma are recorded in the Burgundy register. The sensitivity (57%) for pre-invasive lesions is underestimated while their prevalence is overestimated: the lack of organized screening leads to the loss of prevalent cases. The predictive value of a positive smear is 76% for moderate-severe dysplasia, 85% for in situ carcinoma and over 95% for invasive carcinoma.

Adolescent↗

PubMed1991

[Prognostic factors in hemorrhagic cerebrovascular accidents in a population register].

Since 1985, cases of acute vascular cerebral diseases observed among the inhabitants of the city of Dijon have been systematically recorded: 88 cerebral haemorrhages were reported from 1985 to 1988. Twenty-five variables have been defined from antecedents, clinical and para-clinical data. Seven variables, were statistically associated with death at the end of the first month: age, severity of neurological palsy, meningeal syndrome, coma or comatose state, hyperglycemia and mass effect on CAT-scan. Using a step-down variable selection procedure, two prognostic factors were found: loss of consciousness and advanced age.

Adult↗

PubMed1990

[The Cox model: limitations and extensions].

The proportional hazards model (Cox's model) does not fit the data in many situations. Its limits are reviewed, together with the main goodness-of-fit techniques. Some possibilities of extending the proportional hazards analysis are also described.

Clinical Trials as Topic↗