RESUMEN

We study parametric inference on a rich class of hazard regression models in the presence of right-censoring. Previous literature has reported some inferential challenges, such as multimodal or flat likelihood surfaces, in this class of models for some particular data sets. We formalize the study of these inferential problems by linking them to the concepts of near-redundancy and practical nonidentifiability of parameters. We show that the maximum likelihood estimators of the parameters in this class of models are consistent and asymptotically normal. Thus, the inferential problems in this class of models are related to the finite-sample scenario, where it is difficult to distinguish between the fitted model and a nested nonidentifiable (i.e., parameter-redundant) model. We propose a method for detecting near-redundancy, based on distances between probability distributions. We also employ methods used in other areas for detecting practical nonidentifiability and near-redundancy, including the inspection of the profile likelihood function and the Hessian method. For cases where inferential problems are detected, we discuss alternatives such as using model selection tools to identify simpler models that do not exhibit these inferential problems, increasing the sample size, or extending the follow-up time. We illustrate the performance of the proposed methods through a simulation study. Our simulation study reveals a link between the presence of near-redundancy and practical nonidentifiability. Two illustrative applications using real data, with and without inferential problems, are presented.

Asunto(s)

Modelos de Riesgos Proporcionales , Funciones de Verosimilitud , Simulación por Computador

RESUMEN

This work summarizes the energy generation limits from walking employing a pendulum-based generation system. Self-winding wristwatches have exploited successfully this energy input technique for decades. Pendulum-based planar devices use the rotation to produce energy for inertial generators. Then the oscillations of body motion during locomotion present an opportunity to extract kinetic energy from planar generators. The sinusoidal motion of the center of gravity of the body, on the sagittal and frontal planes, and the limbs swinging are compliant with oscillating devices. Portable biomedical devices can extract energy from everyday walking to extend battery life or decrease battery size. Computer simulations suggest energy availability of 0.05-1.2 mJ on the chest, 0.5-2.5 mJ on the hip and 0.5-41 mJ on the elbow from walking.

Asunto(s)

Fuentes de Energía Bioeléctrica , Caminata/fisiología , Fenómenos Biomecánicos , Simulación por Computador , Humanos

RESUMEN

BACKGROUND: Dementia is a multi-etiologic syndrome characterized by multiple cognitive deficits but not always by the presence of cognitive impairment. Cognitive impairment is associated with multiple non-modifiable risk factors but few modifiable factors. Epidemiologic studies have shown an association between periodontitis, a potentially modifiable risk factor, and cognitive impairment. The objective of this study is to determine whether clinical periodontitis is associated with the diagnosis of cognitive impairment/dementia after controlling for known risk factors, including age, sex, and education level. METHODS: A case-control study was conducted in Granada, Spain, in two groups of dentate individuals aged >50 years: 1) cases with a firm diagnosis of mild cognitive impairment or dementia of any type or severity and 2) controls with no subjective memory loss complaints and a score >30 in the Phototest cognitive test (screening test for cognitive impairment). Periodontitis was evaluated by measuring tooth loss, plaque and bleeding indexes, probing depths, and clinical attachment loss (AL). RESULTS: The study included 409 dentate adults, 180 with cognitive impairment and 229 without. A moderate and statistically significant association was observed between AL and cognitive impairment after controlling for age, sex, education level, oral hygiene habits, and hyperlipidemia (P = 0.049). No significant association was found between tooth loss and cognitive impairment. CONCLUSION: Periodontitis appears to be associated with cognitive impairment after controlling for confounders such as age, sex, and education level.

Asunto(s)

Trastornos del Conocimiento/complicaciones , Demencia/complicaciones , Periodontitis/complicaciones , Factores de Edad , Anciano , Anciano de 80 o más Años , Consumo de Bebidas Alcohólicas , Estudios de Casos y Controles , Trastornos del Conocimiento/clasificación , Demencia/clasificación , Índice de Placa Dental , Escolaridad , Femenino , Humanos , Hiperglucemia/complicaciones , Hiperlipidemias/complicaciones , Masculino , Persona de Mediana Edad , Examen Neurológico , Higiene Bucal , Pérdida de la Inserción Periodontal/clasificación , Índice Periodontal , Bolsa Periodontal/clasificación , Periodontitis/clasificación , Factores de Riesgo , Factores Sexuales , Fumar , Pérdida de Diente/clasificación

RESUMEN

OBJECTIVE: Investigating oral health's relationship with dependency and cognitive state. BACKGROUND: Oral hygiene is poor in the institutionalised elderly. There are problems regarding the oral care of residents having poor mobility or cognitive impairment. MATERIAL AND METHODS: Cross-sectional study involving 135 participants (mean age 85.7, SD 8.8 years) in two categories: nurses doing tooth cleaning and residents doing tooth cleaning. Those cleaned by nurses were categorised as co-operative or unco-operative. The oral hygiene status, presence of caries, retained roots and denture-related stomatitis were recorded. RESULTS: Of the participants, 70% had only natural teeth. The prevalence of caries was 28%. A significant correlation showed that having more teeth gave a poorer Simplified Oral Hygiene Index (OHI-S) (p = 0.018). The number of retained roots increased with the severity of cognitive impairment (p < 0.05). Significant differences were found between nurses or residents doing the tooth cleaning on the OHI-S (p = 0.05) and percentage of dental plaque (p = 0.003). Unco-operative residents had poorer oral hygiene (p = 0.028), more caries (p = 0.008) and were more often moderate-severe cognitive impaired (p = 0.016). CONCLUSIONS: A high percentage of participants had unacceptable oral hygiene. Residents whose teeth were cleaned by the nurses had poorer oral hygiene. Unco-operative residents had the worst oral hygiene and more caries.

Asunto(s)

Trastornos del Conocimiento/epidemiología , Anciano Frágil , Institucionalización , Salud Bucal , Enfermedades Dentales/epidemiología , Anciano , Anciano de 80 o más Años , Conducta Cooperativa , Estudios Transversales , Caries Dental/epidemiología , Placa Dental/epidemiología , Dentaduras/estadística & datos numéricos , Femenino , Hogares para Ancianos , Humanos , Masculino , Persona de Mediana Edad , Noruega/epidemiología , Casas de Salud , Higiene Bucal/enfermería , Higiene Bucal/estadística & datos numéricos , Índice de Higiene Oral , Prevalencia , Caries Radicular/epidemiología , Autocuidado , Estomatitis Subprotética/epidemiología , Raíz del Diente/patología

RESUMEN

The authors conducted a retrospective study of oral squamous cell carcinoma (OSSC) patients in the province of Alava, Spain, to investigate the various epidemiological factors involved. The study included data on 30 patients referred to the Otolaryngology Department of our hospital. The authors identified epidemiological data, including age, symptoms, localization, tumor size, risk factors, tumor stage, treatment and outcome. An elevated percentage of risk factors was found, underlining the importance of early diagnosis. The highest prevalence was in the sixth decade of life. The most frequent symptom was pain, and the localization was in the tongue in 70% of cases. Tumor size ranged from 2 to 3 cm, and 85% of patients underwent surgical resection. Risk factors of smoking and drinking affected 50% of the patients.