Biomedical subjects

Christiane Guinot

Publications and source records attributed to Christiane Guinot.

7 recordsLinked to original sources

PubMed2007

Log-linear non-uniform association models for agreement between two ratings on an ordinal scale.

In agreement studies, when objects are rated independently by two raters (or twice by the same rater), an association between their ratings on two categories arises, reflecting the distinguishability of these two categories for these raters. When ratings are performed on an ordinal scale, this association between ratings on two categories increases when the distance between these categories increases on the ordinal scale. Goodman's log-linear models derived for the analysis of agreement between two raters on an ordinal scale assume that distinguishabilities between adjacent categories are either constant, or a priori fixed. Log-non-linear models that allow variations of the distinguishabilities between adjacent categories along the scale, may lead to difficulties in parameter estimation. This paper describes a new class of log-linear non-uniform association models. These models extend the log-linear uniform association model by allowing variations of distinguishability between adjacent categories (along the scale). These new models are used to analyse ordinal agreement between dermatologists when assessing the severity of different cutaneous signs of ageing on women faces.

Adult↗

PubMed2006

Understanding and reducing variability of SOM neighbourhood structure.

The self-organizing map (SOM) is a nonlinear unsupervised method for vector quantization. In the context of classification and data analysis, the SOM technique highlights the neighbourhood structure between clusters. The correspondence between this clustering and the input proximity is called the topology preservation. We present here a stochastic method based on bootstrapping in order to increase the reliability of the induced neighbourhood structure. Considering the property of topology preservation, a local approach of variability (at an individual level) is preferred to a global one. The resulting (robust) map, called R-map, is more stable relatively to the choice of the sampling method and to the learning options of the SOM algorithm (initialization and order of data presentation). The method consists of selecting one map from a group of several solutions resulting from the same self-organizing map algorithm, but obtained with various inputs. The R-map can be thought of as the map, among the group of solutions, corresponding to the most common interpretation of the data set structure. The R-map is then the representative of a given SOM network, and the R-map ability to adjust the data structure indicates the relevance of the chosen network.

Algorithms↗

PubMed2005

Effect of hormonal replacement therapy on skin biophysical properties of menopausal women.

BACKGROUND/PURPOSE: Hormonal replacement therapy (HRT) has been shown in the past to influence well being as well as several somatic features in menopausal women. The aim of this analysis was to study the effect of HRT on various biophysical properties of the skin of menopausal women. Two sub-samples were built to test the effect (1) of 'short-term' HRT in recently menopausal women (n=15), and (2) the effect of 'medium- and long-term' HRT in menopausal women (n=78). METHODS: The analysis was performed on data from a study of 106 menopausal Caucasian women with apparent healthy skin. Self-report data on the menopausal status, the duration of the menopause, whether or not HRT has been taken and the duration of the HRT were collected. A series of biophysical measurements on the cheek, the forehead and the inner forearm were performed under controlled environmental conditions. Twenty women were menopausal for less than 5 years (eight with HRT for at least 1 year and seven who had never taken HRT) and 86 women for at least 5 years (35 with HRT for at least 5 years and 43 who had never taken HRT). Analyses of covariance with adjustment for age were performed. RESULTS: With regard to skin colour, the measurements in women treated for at least 1 year were significantly higher for red intensity (a*) and lower for brightness (L*) on the forearm as compared with the non-treated women. Furthermore, yellow intensity (b*) mean values were higher on the forehead and the forearm in women treated for at least 5 years compared with the non-treated women. Concerning sebum casual level, the mean values were significantly higher on the forehead and the cheek in women treated for at least 5 years. Regarding skin surface parameters reflecting hydration, the mean values for capacitance on the forehead and the cheek were significantly higher in women treated for at least 5 years. Finally, as regards with skin relief, parameters mean values for amplitude and roughness on the forehead were significantly higher in women treated for at least 5 years. CONCLUSION: The skin colour parameters showed a higher red intensity value in menopausal women who had been treated for at least 1 year. In menopausal women who had been treated for at least 5 years, the biophysical measurements were significantly higher for the parameters reflecting hydration and sebum secretion, which generally decrease after the menopause. These features were associated with higher values for the yellow intensity parameter and the skin relief parameters on the forehead. Our results support the subjective impression and the clinical evaluation concerning the impact of HRT on the development and the evolution of some skin properties after menopause.

Aged↗

PubMed2002

Reference curves based on non-parametric quantile regression.

Reference curves which take time into account, such as those for age, are often required in medicine, but simple systematic and efficient statistical methods for constructing them are lacking. Classical methods are based on parametric fitting (polynomial curves). Semi-parametric methods are also widely used especially in Europe. Here, we propose a new methodology for the estimation of reference intervals for data sets, based on non-parametric estimation of conditional quantiles. The derived methods should be applicable to all clinical (or more generally biological) variables that are measured on a continuous quantitative scale. As an example, we analyse a data set collected to establish reference curves for biophysical properties of the skin of healthy French women. The results are compared to those obtained with Royston's polynomial parametric method and the semi-parametric LMS approach.

Adult↗

PubMed2002

Relative contribution of intrinsic vs extrinsic factors to skin aging as determined by a validated skin age score.

OBJECTIVE: To assess the relative contribution of intrinsic aging vs lifestyle factors to facial skin age. DESIGN: Prospective analysis of a cohort. SETTING: Skin research institute. STUDY SUBJECTS: A cohort of 361 white women (age range, 18-80 years) with apparently healthy skin. MEASUREMENTS: Visual and tactile assessment of facial skin features. RESULTS: Twenty-four skin characteristics were used to build a skin age score (SAS). The relationship between the SAS and chronological age followed a linear model with 2 plateaus--1 before age 30 years and 1 after age 71 years. An analysis was performed to determine whether certain lifestyle habits known to have effects on skin aging were related to the discrepancies between chronological age and the SAS. Significant effects were identified for phototype, body mass index, menopausal status, degree of lifetime sun exposure, and number of years of cigarette smoking. However, these factors accounted for only 10% of the discrepancies. Moreover, most skin characteristics used reflected changes understood to represent intrinsic aging rather than photodamage or other extrinsic factors. CONCLUSIONS: An SAS can be generated from multiple discrete signs evaluated on facial skin and is an informative tool for quantifying skin aging. The SAS is influenced by factors already recognized to affect the aging phenotypes; however, factors related to the rate of intrinsic aging, presumably genetic in character, seem to play a larger role than previously suspected.

Adolescent↗

PubMed2000

Transepidermal water loss, temperature and sebum levels on women's facial skin follow characteristic patterns.

BACKGROUND/AIMS: The aim of this study was to compare the biophysical properties of different facial zones. METHODS: We investigated transepidermal water loss (TEWL), skin temperature and sebum casual level (CL) on 90 adjacent test sites distributed on the forehead, cheeks and chin of five women. RESULTS: All three parameters showed a symmetrical distribution around the facial median line. Only minor variations of individual values were found within the forehead and the chin areas. In contrast, the cheeks exhibited a distinct gradient with highest values in the paranasal zones and lowest on the cheek bones for all of the three parameters. The mean values on both cheeks of a given individual were nearly identical, and the patterns within the two cheeks were superimposable. Both CL and skin temperature distributions pointed out a "T-zone" with highest values on the forehead, on the chin and on the median part of the cheek. CONCLUSIONS: Our data demonstrate that biophysical skin properties differ considerably between different facial areas but that they follow a characteristic distribution.

Journal Article↗

PubMedDate not supplied

Sun-reactive Skin Type in 4912 French adults participating in the SU.VI.MAX study.

Phototype classifications were initially developed in an attempt to predict the skin reactions of patients to phototherapy and are now widely used to advise individuals with regard to sun protection. A transversal study was conducted on the SU.VI.MAX cohort to estimate the frequency of sun-reactive skin features in a large, general adult population-based sample, and to describe the associations between these features. The data were collected 3 years after the beginning of the SU.VI.MAX nutritional intervention study on 4912 volunteers (2868 women aged 35-60 years and 2044 men aged 45-60 years). A multiple correspondence analysis was performed to study the associations between the features. The results showed that these features correspond to a one-dimensional phenomenon, which allowed us to establish a score to summarize skin sensitivity to sun exposure. Furthermore, we found a link between gender and phototype using the Césarini classification (phototype > or = IV: 37% of women, 47% of men). The analysis of the relationship with sun-reactive skin features and the score revealed the same trend. Phenotypic evaluation appears to be a good estimator of skin sensitivity to sun exposure for clinical screening or for use in research, and is easy to collect at a lower cost. Moreover, the sun sensitivity difference between gender should be considered in education about photoprotection.

Adult↗