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Abstract: The objective of this work was to determine the number of plants required to model corn grain yield (Y) as a function of ear length (X1) and ear diameter (X2), using the multiple regression model Y = β0 + β1X1 + β2X2. The Y, X1, and X2 traits were measured in 361, 373, and 416 plants, respectively, of single-, three-way, and double-cross hybrids in the 2008/2009 crop year; and in 1,777, 1,693, and 1,720 plants, respectively, of single-, three-way, and double-cross hybrids in the 2009/2010 crop year, totaling 6,340 plants. Descriptive statistics were calculated, and frequency histograms and scatterplots were created. The sample size (number of plants) for the estimate of the β0, β1, and β2 parameters, of the residual standard error, the coefficient of determination, the variance inflation factor, and the condition number between the explanatory traits of the model (X1 and X2) were determined by resampling with replacement. Measuring 260 plants is sufficient to adjust precise multiple regression models of corn grain yield as a function of ear length and ear diameter. The Y = -229.76 + 0.54X1 + 6.16X2 model is a reference for estimating corn grain yield.

El presente trabajo analiza los efectos de la aplicación de la técnica de "jigsaw", puzzle o rompecabezas de Aronson en la adquisición de competencias por parte de estudiantes universitarios. Más concretamente buscamos determinar qué competencias sistémicas, instrumentales e interpersonales se adquieren más fácilmente al implantar "jigsaw" en el proceso de enseñanza-aprendizaje. Los resultados alcanzados muestran que esta técnica de aprendizaje cooperativo facilita en mayor medida la adquisición de competencias sistémicas e instrumentales en comparación con las interpersonales. Dentro de las competencias sistémicas, la que desarrollan con más facilidad los alumnos es la denominada metareflexión; es decir, el aprendizaje progresivo por repetición. En el grupo de competencias instrumentales, destacan la interacción entre compañeros, las habilidades comunicativas del alumno, la participación, la ayuda en la resolución de conflictos entre compañeros surgidos durante la dinámica y la mejora de la instrucción directa. Finalmente, en relación a las competencias interpersonales, la más desarrollada es el sentido de la responsabilidad del alumno. || The aim of this study was to determine the effects of the cooperative ``jigsaw'' method on generic competence-based training by university students. This specifically sought to understand how systemic, instrumental and interpersonal competences are more easily acquired by adopting ``jigsaw'' in the teaching-learning procedure. The results reveal that this cooperative learning method makes the development of systemic and instrumental competences easier to a greater extent than interpersonal ones. Meta-reflection or progressive rote learning achieved a highest score among systemic competences. Focusing our attention on the instrumental dimension, peer interaction, students' communication skills, participation, resolution of peer conflicts and direct instruction, these competences sty out from the rest. Finally, responsibility was the easiest competence in the interpersonal dimension.

INTRODUCCIÓN El desarrollo de proyectos de investigación suele demandar del uso de herramientas matemáticas para expresar en términos numéricos o gráficos diversas magnitudes, tales como frecuencias, diferencias, o asociaciones. OBJETIVOS El presente estudio se propone describir la utilización que se hace de las herramientas estadísticas básicas, haciendo especial énfasis en el uso de las pruebas de significación estadística y los intervalos de confianza, para la presentación de resultados de investigación en los artículos publicados en una reconocida revista de la salud pública en Colombia. MÉTODOS Se realizó una revisión de los 84 artículos originales publicados en dicha revista entre 2013 y 2014. RESULTADOS El recurso más empleado es la utilización de análisis de frecuencias (89,3%), seguido de los valores p (65,5%) y los intervalos de confianza (53,6%); el 48,9% de los artículos utiliza a la vez intervalos de confianza y valores p para la presentación de resultados y el 29,8% ninguno de los dos. El 16,7% de los artículos sólo utiliza valores p y el 4,8% sólo intervalos de confianza. CONCLUSIONES La estadística descriptiva es una herramienta que se utiliza con asiduidad en la presentación de resultados y que las críticas y advertencias sugiriendo que se evite el uso exclusivo de las pruebas de significación estadística en la presentación de resultados no son cabalmente tenidas en cuenta en el análisis y presentación de los resultados de investigación.

Em uma área de Terra Roxa Estruturada Latossólica de Piracicaba,SP, foram coletadas 250 amostras de solo com estrutura indeformada à profundidade de 25 cm, segundo um espaçamento regular de 5 m. As amostras foram submetidas às tensões de 5xl0²; 1x10³; 6x10³; 1x10(4) (Funil de Haines) e pressões de 3x10(4); 8x10(4); 3x10(5) e 1,5x10(6) Pa (Câmara de Pressão de Richards) para obtenção das relações entre potencial mátrico e umidade do solo. Assim foram obtidos duzentos e cinqüenta valores de umidade à base de massa (variável dependente) para cada valor de tensão fixado (variável independente), num total de dois mil resultados experimentais. Utilizaram-se medidas de posição (moda, mediana e média aritmética), variabilidade (amplitude total, amplitude interquartil, desvio padrão, coeficiente de variação, assimetria, curtose e limites de confiança em torno da média aritmética) e número de amostras para estimar a média da umidade a um dado nível de probabilidade, com os seguintes objetivos: a) verificar o quanto as distribuições de probabilidade dos valores de umidade para as diferentes tensões consideradas se afastam da distribuição normal e, consequentemente, investigar qual a melhor medida de posição para representar o conjunto; b) quantificar a variabilidade a cada tensão considerada, identificando as mais problemáticas no estudo da retenção da água no solo, ao lado de uma analise da sensibilidade das medidas, através do cálculo do número necessário de amostras para estimar a média (desconsiderando-se a dependência espacial das amostras). A análise dos resultados obtidos permitiu concluir que as umidades às tensões de 5x10² e 1x10³ Pa apresentaram distribuição com assimetria exagerada e portanto há que se tomar cuidado com o uso da média aritmética como medida de posição. O descarte de amostras-problema, baseado na análise física dos resultados, permitiu, no entanto, melhor aproximação da normalidade para estas tensões, indicando que se deve sempre dar preferência à curva completa de retenção de água no solo e não apenas a dois ou três pontos de interesse imediato, como é feito usualmente. As umidades às várias tensões utilizadas apresentaram baixo coeficiente de variação (< 10%), quando comparadas a outras medidas de propriedades físicas do solo.In an area of "Terra Roxa Estruturada Latossólica" (Rhodic Kanhapludalf), in Piracicaba, SP, Brazil (20° 42' 30" S, 47° 38' 00" W, 576 m), 250 undisturbed soil samples were collected at 25 cm soil depth, according to a regular grid of spacing of 5 m, resulting a network of 25 Unes and 10 columns. These samples were used to determine 250 soil water retention curves each one with eigth experimental points, using Haines funnels (tensions of 5xl0², 1x10³, 6x10³ and 1x10(4) Pa) and Richards pressure chambers (pressures of 3x10(4), 8x10(4),3x10(5) and 1x10(6) Pa), totalizing two thousand values. Position measurements (mode, median and arithmetic mean), variability (total amplitude, interquartil amplitude, standard deviation, coefficient of variation, assimetry, kurtosis and confident limits around the mean) and number of samples to estimate the mean of the soil water content at a specific probability level, were used with the following objectives: a) to verify how close to the normal distribution are the values of soil water content for the different considered tensions and hence, to investigate what is the best position measurement; b) to quantify the variability in each considered tension, identifying the most problematic in the study of soil-water retention and also to analyse the measurement sensibility through the calculation of the necessary number of samples to estimate the mean (assuming a spatial independence of the samples). From the analysis of the obtained results, it could be concluded that the soil-water content values corresponding to tensions of 5x10² and 1x10³ Pa showed very skewed distributions, so that care should be taken in using the arithmetic mean as a position measurement. The neglection of problem-samples, based on the physical analyses of results, allowed a better aproximation to the normal distributions for these tensions, indicating that a complete soil-water retention curve should always be prefered in the place of only two or three points of restricted interest as it is normally done. Soil-water contents corresponding to the several considered tensions showed low coefficients of variation (< 10 %) as compared to other soil physical measurements.

Introduction: Research projects use statistical resources to express in numerical or graphic terms different magnitudes like frequencies, differences or associations., Objectives: The purpose of this paper is to describe the statistics tools utilization, with special emphasis in the use of conventional statistical tests and confidence intervals, to communicate results in a renowned public health peer reviewed journal in Colombia., Methods: We included the 84 articles published in the journal between 2013 and 2014., Results: The most used resource is frequency analysis (89.3%), followed by p values (65.5%) and confidence intervals (53.6%); 48.9% of the papers used confidence intervals together with p values; 29.8% use neither of them; 16.7% of the articles only used p values and 4.8% only confidence intervals., Conclusions: Descriptive statistics is a tool widely used in research results presentation; the critics and caveats suggesting to avoid the exclusive use of the statistical signification test in the results presentation are not followed in the analysis and presentation of the research results.