Clustering Disjoint HJ-Biplot: A new tool for identifying pollution patterns in geochemical studies.

This paper introduces a new mathematical algorithm termed Clustering Disjoint HJ-Biplot (CDBiplot), which searches for the underlying data structure in order to find the best classification of the object groups in a reduced space. To this end, disjoint factorial axes are generated, in which each variable only contributes to the formation of one factorial axis. A graphical representation of the individuals and variables is performed using the HJ-Biplot method. In order to facilitate the use of this new method within any practical context, a function in the language R has been developed. This work applies the CDBiplot to study an environmental geochemistry case involving environmental pollution in river surface sediments. The study focuses on an area close to an important mining and metallurgical site, where sediments share a similar geological origin and chemical composition. The algorithm permitted a detailed study of the geochemical interactions and performed an excellent separation of the samples. Thus, the groups obtained were formed according to a similar geological origin, location, and nature of the anthropogenic inputs based only on chemical composition data. These results allowed clear identification of the sources of pollution and the delimitation of the polluted zones. All things considered, we conclude that the proposed algorithm is a powerful tool for studying environmental geochemistry data sets, and suggest that the application of this methodology be extended to other research fields.

Comparative validity of the OIDP and OHIP-14 in describing the impact of oral health on quality of life in a cross-sectional study performed in Spanish adults.

OBJECTIVES: We aimed to compare the utility and validity of two popular socio-dental indicators (OIDP and OHIP-14) for describing the impact of oral conditions on quality of life applied simultaneously. STUDY DESIGN: We recruited a consecutive sample of 270 healthy Spanish workers visiting the Employment Risk Prevention Centre for a routine medical check-up. OHIP-14 was self-completed before the oral examination and the face to face interview of the OIDP was performed. Both instruments were compared by evaluating its reliability and its validity. RESULTS AND CONCLUSIONS: The standardised Cronbach alphas for OHIP-14 and OIDP were 0.89 and 0.74 respectively. OIDP showed lower face validity but higher content validity than OHIP-14. Both indicators showed high construct and criterion validity, since individuals perceiving need for dental treatment or having any complaint about their mouth obtained significantly higher total OIDP and OHIP scores than their counterparts. The prevalence of impacts was much higher using the OHIP (80.7%) than the OIDP (27.8%).

Impact of prosthodontic status on oral wellbeing: a cross-sectional cohort study.

To assess the impact of the prosthodontic status on oral health-related quality of life and satisfaction. We performed a cohort study at the University Clinic in Salamanca in which a group requesting prosthetic treatment (P0; n = 31) was compared with a group treated with conventional prostheses (P1; n = 29) and a control group (C; n = 18) not requesting or treated with prostheses. A clinical examination for the presence of caries, periodontal disease and edentulism was carried out. An assessment was made on the impact on the quality of life employing the oral impacts on daily performance-Spanish version and the oral health impact profile 14-Spanish version, and wellbeing was assessed by the self-rated satisfaction on a 0-10 scale. The P0 cohort was significantly less satisfied and suffered a greater level of impact as regard their quality of life than the other cohorts. The main benefit of conventional prosthetic treatment was perceived by most of the treated patients (P1) in dimensions related to chewing, the aesthetic function and the assessment of the general state of the mouth. However, an unexpected proportion of patients underwent a worsening of their oral wellbeing after prosthetic treatment, mainly in the chewing ability (23%) and pain discomfort (19%) dimensions. Satisfaction and quality of life were higher in the treated group (P1) and controls (C) than in those requesting prosthetic treatment (P0).

The Biplot as a diagnostic tool of local dependence in latent class models. A medical application.

Latent class models (LCMs) can be used to assess diagnostic test performance when no reference test (a gold standard) is available, considering two latent classes representing disease or non-disease status. One of the basic assumptions in such models is that of local or conditional independence: all indicator variables (tests) are statistically independent within each latent class. However, in practice this assumption is often violated; hence, the two-LCM fits the data poorly. In this paper, we propose the use of Biplot methods to identify the conditional dependence between pairs of manifest variables within each latent class. Additionally, we propose incorporating such dependence in the corresponding latent class using the log-linear formulation of the model.

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