Pérdida de información a causa de la censura

Tesis Univ. Compl. Madrid. Dpto. de Estadística e Investigación Operativa. Dirigida por Julián de la Horra Navarro, leída en Madrid ca. 1987.Depto. de Estadística e Investigación OperativaFac. de Ciencias MatemáticasTRUEProQuestpu

Lempel-Ziv complexity in schizophrenia: A MEG study

Objective The neurodevelopmental–neurodegenerative debate is a basic issue in the field of the neuropathological basis of schizophrenia (SCH). Neurophysiological techniques have been scarcely involved in such debate, but nonlinear analysis methods may contribute to it. Methods Fifteen patients (age range 23–42 years) matching DSM IV-TR criteria for SCH, and 15 sex- and age-matched control subjects (age range 23–42 years) underwent a resting-state magnetoencephalographic evaluation and Lempel–Ziv complexity (LZC) scores were calculated. Results Regression analyses indicated that LZC values were strongly dependent on age. Complexity scores increased as a function of age in controls, while SCH patients exhibited a progressive reduction of LZC values. A logistic model including LZC scores, age and the interaction of both variables allowed the classification of patients and controls with high sensitivity and specificity. Conclusions Results demonstrated that SCH patients failed to follow the “normal” process of complexity increase as a function of age. In addition, SCH patients exhibited a significant reduction of complexity scores as a function of age, thus paralleling the pattern observed in neurodegenerative diseases. Significance Our results support the notion of a progressive defect in SCH, which does not contradict the existence of a basic neurodevelopmental alteration. Highlights ► Schizophrenic patients show higher complexity values as compared to controls. ► Schizophrenic patients showed a tendency to reduced complexity values as a function of age while controls showed the opposite tendency. ► The tendency observed in schizophrenic patients parallels the tendency observed in Alzheimer disease patients

On the relative efficiency of grouped and censored survival data

The relative efficiency of a censored experiment compared with the corresponding noncensored experiment for inference is examined for grouped survival data. It is assumed that observations are randomly right-censored. The case of fixed censoring is also considered

Una medida matricial para la comparación de experimentos censurados

En este trabajo se desarrolla un método de comparación de experimentos con datos censurados. Dicho método se basa en la evaluación de la pérdida de información que se produce en estudios de supervivencia y fiabilidad cuando los tiempos de vida se censuran aleatoriamente por la derecha. Se supone que la distribución del tiempo de vida depende de un parámetro k-variante desconocido θ; y se usa la matriz de Fisher como medida de información apropiada acerca de θ. Se propone una medida matricial de la pérdida de información mediante la generalización de la medida real correspondiente, y se examinan sus propiedades. Se definen medidas reales de la pérdida de información a través de funciones adecuadas de los autovalores de dicha medida matricial

Joint effect of noise, personality and environmental factors on the intelligibility of speech

The performance of students in speech intelligibility tests is influenced by individual characteristics such as sex and age, personality factors such as neuroticism (N), extraversion, attention and sensitivity to noise, and environmental conditions such as the location of the scholars in the classroom (LI), the location of the classroom itself with regard to extraneous noise (LO) and background noise (BN). The first aim of this study was to analyse the role of these factors in predicting performance. From a mathematical point of view the problem was to establish a model to reflect accurately the relationship between the expected proportion of successes and a set of covariates. We used a logistic regression model mainly because of its high mathematical flexibility. A further aim was to study in depth methodological questions such as the choice and assessment of the model, including its extension to a random-effects model. One hundred and seventy students participated in the study. The results indicate that only four of the factors studied had any significant bearing upon their performance: N, LI, BN and LO, and that the effect of the classroom on performance was a random one. The covariate pattern corresponding to the best performance is given by the following levels : (N) high, (LI) front row, (LO) playground and (BN) normal. For this pattern the estimated proportion of successes is 0.6

Embryonic cardiac morphometry in Carnegie stages 15-23, from the Complutense University of Madrid Institute of Embryology Human Embryo Collection

Aims: We performed a morphometric study of cardiac development on human embryos to complement the scarce data on human embryonic cardiac morphometry and to attempt to establish, from these, algorithms describing cardiac growth during the second month of gestation. Methods: Thirty human embryos from Carnegie stages 15-23 were included in the study. Shrinkage and compression effects from fixation and inclusion in paraffin were considered in our calculations. Results: Growth of the cardiac (whole heart) volume and volume of ventricular myocardium through the Carnegie stages were analysed by ANOVA. Linear correlation was used to describe the relationship between the ventricular myocardium and cardiac volumes. Comparisons of models were carried out through the R2 statistic. The relationship volume of ventricular myocardium versus cardiac volume is expressed by the equation: cardiac volume = 0.6266 + 2.4778 volume of ventricular myocardium. The relationship cardiac volume versus crown-rump length is expressed by the equation: cardiac volume = 1.3 e 0.126 CR length, where e is the base of natural logarithms. Conclusion: At a clinical level, these results can contribute towards the establishment of a normogram for cardiac development, useful for the design of strategies for early diagnosis of congenital heart disease. They can also help in the study of embryogenesis, for example in the discussion of ventricular trabeculation

Recruitment of occipital cortex during sensory substitution training linked to subjective experience of seeing in people with blindness

Over three months of intensive training with a tactile stimulation device, 18 blind and 10 blindfolded seeing subjects improved in their ability to identify geometric figures by touch. Seven blind subjects spontaneously reported 'visual qualia', the subjective sensation of seeing flashes of light congruent with tactile stimuli. In the latter subjects tactile stimulation evoked activation of occipital cortex on electroencephalography (EEG). None of the blind subjects who failed to experience visual qualia, despite identical tactile stimulation training, showed EEG recruitment of occipital cortex. None of the blindfolded seeing humans reported visual-like sensations during tactile stimulation. These findings support the notion that the conscious experience of seeing is linked to the activation of occipital brain regions in people with blindness. Moreover, the findings indicate that provision of visual information can be achieved through non-visual sensory modalities which may help to minimize the disability of blind individuals, affording them some degree of object recognition and navigation aid

Magnetoencephalographic parietal δ dipole density in mild cognitive impairment: Preliminary results of a method to estimate the risk of developing Alzheimer disease

Background: Subjects with mild cognitive impairment (MCI) are at a higher risk of experiencing Alzheimer disease (AD). Magnetoencephalographic temporoparietal dipole densities of low-frequency activity are good predictors of individuals' cognitive status, and might be a useful tool to investigate the conversion from MCI to AD. Objective: To investigate the role of low-frequency dipole densities as predictors of the risk of developing AD. Design: Whole-head magnetoencephalographic recordings were obtained from 19 probable AD patients, 17 MCI patients, and 17 healthy control subjects. The generators of focal magnetic slow waves were located using a single moving dipole model. Results: Left parietal δ dipole density permitted a reliable classification of AD and MCI patients. The MCI patients were divided into 2 groups based on the median left parietal δ dipole density, and were followed up for 2 years. The estimated relative risk of conversion to AD was increased by 350% in those MCI patients with high left parietal δ dipole density scores. Conclusions: Results confirmed the important role of parietal δ dipole density in the evaluation of AD and MCI. A magnetoencephalographic-based assessment of AD and MCI patients might be considered a useful clinical test in the near future