213,406 research outputs found
Maximally selected chi-square statistics and umbrella orderings
Full text linkBinary outcomes that depend on an ordinal predictor in a non-monotonic way are common in medical data analysis. Such patterns can be addressed in terms of cutpoints: for example, one looks for two cutpoints that define an interval in the range of the ordinal predictor for which the probability of a positive outcome is particularly high (or low). A chi-square test may then be performed to compare the proportions of positive outcomes in and outside this interval. However, if the two cutpoints are chosen to maximize the chi-square statistic, referring the obtained chi-square statistic to the standard chi-square distribution is an inappropriate approach. It is then necessary to correct the p-value for multiple comparisons by considering the distribution of the maximally selected chi-square statistic instead of the nominal chi-square distribution. Here, we derive the exact distribution of the chi-square statistic obtained by the optimal two cutpoints. We suggest a combinatorial computation method and illustrate our approach by a simulation study and an application to varicella data
Maximally selected chi-square statistics and binary splits of nominal variables
Full text linkWe address the problem of maximally selected chi-square statistics in the case of a binary Y variable and a nominal X variable with several categories. The distribution of the maximally selected chi-square statistic has already been derived when the best cutpoint is chosen from a continuous or an ordinal X, but not when the best split is chosen from a nominal X. In this paper, we derive the exact distribution of the maximally selected chi-square statistic in this case using a combinatorial approach. Applications of the derived distribution to variable selection and hypothesis testing are discussed based on simulations. As an illustration, our method is applied to a pregnancy and birth data set
Maximally selected chi-square statistics for at least ordinal scaled variables
Full text linkThe association between a binary variable Y and a variable X with an at least ordinal measurement scale might be examined by selecting a cutpoint in the range of X and then performing an association test for the obtained 2x2 contingency table using the chi-square statistic. The distribution of the maximally selected chi-square statistic (i.e. the maximal chi-square statistic over all possible cutpoints) under the null-hypothesis of no association between X and Y is different from the known chi-square distribution. In the last decades, this topic has been extensively studied for continuous X variables, but not for non-continuous variables with an at least ordinal measurement scale (which include e.g. classical ordinal or discretized continuous variables). In this paper, we suggest an exact method to determine the distribution of maximally selected chi-square statistics in this context. This novel approach can be seen as a method to measure the association between a binary variable and variables with an at least ordinal scale of different types (ordinal, discretized continuous, etc). As an illustration, this method is applied to a new data set describing pregnancy and birth for 811 babies
CHI
No full textChi es la energía vital que mantiene el equilibrio de la salud espiritual, emocional, mental y física de una persona. Como seres humanos estamos en un constante crecimiento y aprendizaje y no podemos hacerlos solos, por ello en Chi Wellness Center fomentamos la importancia de la comunidad. El wellness como un estilo de vida se enfoca en un balance de los cuatro pilares del Chi que deben ejercitarse simultáneamente y practicarse a diario.https://sciencevalue.udit.es/tfg_interiores_producto/1199/thumbnail.jp
Chi Kung, el arte de dejar que suceda
No full textCon Alejandra Bojacá, fisioterapeuta, hablamos sobre su experiencia en la práctica del Chi Kung y como este arte milenario nos aporta a estos momentos en que necesitamos la calma. Alejandra quien es formada en medicina tradicional china ha incorporado la práctica del Chi Kung a su vida personal y profesional
Playful toothbrush: Ubicomp technology for teaching tooth brushing to kindergarten children.
No full text
Generalized Chi distribution for non-integer degrees of freedom in modelling biological collectivities
No full text[EN] This article aims to expand the practical potential of the Chi and Chi-square distributions by extending their applicability to non-integer degrees of freedom, k. The study has two main objectives:
first, to explore and leverage the relationship between the Chi, Chi-square, and Gamma distributions to interpret non-integer degrees of freedom; and second, to apply this framework to real survival-time
data in the context of biological and health sciences. Three specific cases are analyzed: the germination times of Pinus tropicalis Morelet seeds cultivated in western Cuba; the interval between infection by
virulent tuberculous bacilli and death from tuberculosis in guinea pigs; and the period from the onset of symptoms to death due to COVID-19 in patients in Mexico during 2020. A parameter estimation was performed by maximum likelihood (MLE), and the optimal value of k was found to be non-integer in all cases.We would like to acknowledge funding from the Generalitat Valenciana (Spain) through the PROMETEO CIPROM/2023/32 grant, and from the Agencia Estatal de Investigacion (Spain) through ¿the PID2022-142407NB-I00 and PID2024-162480OB-I00 grants. The work of S.S. is partially supported by DGAPA-UNAM (Mexico) Project No. IN103522. The author A.G.C. was supported ¿ by a contract of the Programa de Ayudas de Investigacion y Desarrollo (PAID-01-24), Universitat ¿Politecnica de Val ` enciaCastro-Palacio, Juan Carlos;Fernández de Córdoba, Pedro;Álvaro;Isidro, J.M.;Noverques-Medina, Aina;Orellana-Panchame, MF.;Sahu, S.... (2025). Generalized Chi distribution for non-integer degrees of freedom in modelling biological collectivities. AIMS Mathematics. 10(10):25033-25048. https://doi.org/10.3934/math.20251109S2503325048101
Chi-squared test P-value for each TFBS motif in every cell type.
No full textChi-squared test P-value for each TFBS motif in every cell type.</p
Pyridyl Azolate Based Luminescent Complexes: Strategic Design, Photophysics, and Applications
No full text- …
