Robustez de cinco estadísticos univariados para analizar diseños Split-Plot en condiciones adversas / Robustness of five univariate statistics in analyzing Split-Plot desings under adverse conditions

En esta investigación examinamos el comportamiento de cinco estadísticos univariados para analizar datos en un diseño Split-Plot. Cuatro de ellos asumen que la matriz de desviación subyacente es no esférica. Sin embargo, existe una clara distinción entre dos alternativas, dos procedimientos presuponen que la correlación entre los datos no sigue un patrón determinado y otros dos asumen que existe autocorrelación serial de primer orden. Todos ellos fueron comparados con respecto a su robustez para poner a prueba las fuentes de variación intra-sujeto (tratamiento e interacción) bajo distribución no normal en ausencia de esfericidad y en ambas situaciones, bajo correlación serial de primer orden y bajo correlación arbitraria. Los resultados muestran que cuando la distribución es no normal simétrica todos los procedimientos muestran una tasa de error de Tipo I similar a la obtenida bajo distribución normal. Conforme el grado de sesgo y curtosis incrementa, todos los procedimientos experimentan una alteración en su estimación de la tasa de error de Tipo I y que depende de la estructura de la matriz de covarianza que subyace a los datos. En el conjunto de condiciones sometidas a estudio los procedimientos más robustos fueron HCH, JN y LEC.

In this research we examine the behaviour of five univariate statistics for analyzing the data of a Split-Plot design. Four of them assume that the dispersion matrix underlying is not spherical. However, they do so with a clear distinction between two alternatives, insofar as two of them presuppose that the correlation between the data does not have a certain structure and other two assume that there exists first-order serial autocorrelation. All of them were compared with regard to their robustness to test the sources of variation within-subject (treatment and interaction) under non-normality in the absence of sphericity, both when there was first-order serial autocorrelation and when the underlying correlation was arbitrary. The results show that when the distribution is non-normal symmetric all the procedures show a Type I error rate similar to the obtained one under normal distribution. As the degree of skewness and kurtosis increases, all the procedures experience an alteration in their estimation of the Type I error rate and that it depends on the structure of covariance matrix underlying in the data. In the set of conditions submitted to study the most robust procedures were HCH, JN and LEC.

Procedimientos estadísticos alternativos para evaluar la robustez mediante diseños de medidas repetidas / Alternative satatistical procedures to assess the robustness using repeated measures designs

The purpose of this investigation was assessing the robustness of a series of new procedures under the traditional ANOVA approach to analyze some data corresponding to repeated measures by means of Monte Carlo simulation. In order to study the efficacy of these procedures for the control of Type I rate of errors, four variables were handled: sample size; structure of dispersion matrixes; relationship between the group sizes and the dispersion matrices, and population distribution pattern. Results suggest that the Improved General Approach, Proc Mixed program with the Kenward-Roger solution, Brown-Forsythe and Welch James procedures offer a very good behavior to control the Type I rate of errors both for the main effect of the measurement opportunities as well as the effect of interaction, under all the assessed conditions.

El propósito de la presente investigación radica en evaluar la robustez de una serie de nuevos procedimientos alternativos al tradicional enfoque ANOVA para analizar datos de medidas repetidas mediante el método de simulación Monte Carlo. Para estudiar la eficacia de estos procedimientos en el control de las tasas de error de Tipo I se manipularon cuatro variables: tamaño de la muestra, estructura de las matrices de dispersión, relación entre el tamaño de los grupos y el de las matrices de dispersión y forma de distribución de la población. Los resultados obtenidos sugieren que los procedimientos Aproximación General Mejorada, Proc Mixed con la solución Kenward-Roger, Brown-Forsythe y Welch James ofrecen un muy buen comportamiento para controlar las tasas de error de Tipo I, tanto para el efecto principal de las ocasiones de medida como para el efecto de la interacción, bajo todas las condiciones evaluadas.

Diferencias individuales en dietantes crónicos: Influencia de los sistemas motivacionales en la alimentación / Differences among chronic restrained eaters: the influence of motivational systems

Background: Restrained eaters (RE) are individuals who restrain their food intake on a regular basis as they are frightened to gain weight. However, they tend to overeat under conditions of anxiety. It has been shown that RE possess a behavioral inhibition system that is more active in tonic terms, which would partially explain their affective vulnerability. Even so, the influence of variations in the activation levels of the emotional systems on the eating behavior of a RE is still unknown. Our hypothesis is that variations of such systems will give place to two types of RE: a successful or a non-successful one. Aim: To assess the influence of variations on the activation of motivational systems in food intake of RE. Materials and methods: As part of a factorial experimental design, 105 undergraduate university students were part of an experimental test for inducting food intake. Then they reported their levels of dietary restraint and their emotional behavioral preferences. Results: Differences in the activation of motivational systems were significantly related to differences in food intake (F= 7.210; p= 0.001). Additionally, food intake for those RE with a predominant inhibition system tended to be higher than for those with a more active approach system, though the latter did not reach a significant difference (F=0.718; p=0.399). Conclusions: Although more investigations are required, our data suggest that the success of retaining the diet among the RE would depend on their profile of affective reactivity (affective style). There are putative implications for research on anorexia and obesity.

Evaluación del efecto de una intervención cognitivo-conductual sobre los niveles de presión arterial en adultos mayores hipertensos bajo tratamiento médico / Effects of a cognitive-behavioral intervention on blood pressure of hypertensive elderly subjects

Background: Cognitive and behavior therapy can be used as an adjunct to medications to reduce blood pressure in hypertensive patients. Aim: To design a brief psychological intervention for hypertensive patients and assess its effects on blood pressure. Material and methods: Thirty eight hypertensive subjects (35 women, age range 63-77 years) were studied. They were randomly divided in a control and experimental group. The latter group attended eight sessions of a cognitive-behavioral intervention, lasting two hours each, during one month. In each session, subjects were trained in relaxation techniques, cognitive modeling and psycho education. The main outcome assessed was a change in blood pressure levels. Results: In the experimental group, there was a significant reduction from baseline to the second post test assessment, in systolic and diastolic blood pressure levels from 134±9 to 123±8 mmHg and from 87±5 to 73±6 mmHg, respectively. Conclusions: The psychological intervention used in the present study achieved significant reductions in blood pressure levels in this group of hypertensive subjects.

Intervenciones psicológicas basadas en la evidencia para la prevención de la delincuencia juvenil: un programa de habilidades sociales en ambientes educativos / Psychological interventions based on juvenile delinquency prevention evidence: a social skills program in educational settings

Seis menores en conflicto con la justicia recibieron un programa de habilidades sociales para ampliar repertorios conductuales socialmente deseables y con ello facilitar su ajuste social y personal a diferentes ambientes. El diseño utilizado para evaluar la implementación de un tratamiento eficaz es el de línea base múltiple. El análisis realizado se hace en términos de significación clínica y estadística. Los resultados permiten concluir que los cambios observados se deben al tratamiento clínico implementado y que las políticas sociales para abordar el problema debieran considerarse para su aplicación en el largo plazo. Estas precauciones se han tomado por el hecho de ser un estudio de series temporales cortas y con ello evitar conclusiones apresuradas a partir de los efectos del ôtrauma ocularõ (Kazdin, 1984).