Un aspecto importante en la metodología de la investigación, es el cálculo de la cantidad de participantes que deben incluirse en un estudio. El tamaño de muestra permite a los investigadores saber cuántos individuos son necesarios estudiar, para poder estimar un parámetro determinado con el grado de confianza deseado, o el número necesario para poder detectar una determinada diferencia entre los grupos de estudio, suponiendo que existiese realmente.El cálculo del tamaño de la muestra es una función matemática que expresa la relación entre las variables, cantidad de participantes y poder estadístico.La muestra de un estudio debe ser representativa de la población de interés. El objetivo principal de seleccionarla es hacer inferencias estadísticas acerca de la población de la que proviene. La selección debe ser probabilística.Los factores estadísticos que determinan el tamaño de la muestra son: hipótesis, error alfa, error beta, poder estadístico, variabilidad, pérdidas en el estudio y el tamaño del efecto. Se revisan las fórmulas utilizadas para el cálculo del tamaño de la muestra en las situaciones más frecuentes en investigación, así como la revisión de fórmulas para un cálculo más rápido. Se incluyen ejemplos de investigación en educación médica. También se revisan aspectos importantes como: tamaño de la muestra para estudios piloto, estrategias para disminuir el número necesario de sujetos, y software para el cálculo del tamaño de muestra.

Tuberculosis in developing countries is still an important cause of skin lesions which must be studied via histopathological examination and culture due to their low bacillary load. A PCR test is necessary to obtain faster confirmation of the disease and to establish an early, specific and effective treatment.

ObjectiveThe aim of this study was to estimate the heritability (h2) and genetic correlation (ρG) between GERD symptoms severity, metabolic syndrome components, and inflammation markers in Mexican families.MethodsCross-sectional study which included 32 extended families resident in Mexico City. GERD symptoms severity was assessed by the ReQuest in Practice questionnaire. Heritability and genetic correlation were determined using the Sequential Oligogenic Linkage Analysis Routines software.Results585 subjects were included, the mean age was 42 (±16.7) years, 57% were women. The heritability of the severity of some GERD symptoms was h2 = 0.27, 0.27, 0.37, and 0.34 (p-value <1.0x10-5) for acidity complaints, lower abdominal complaints, sleep disturbances, and total ReQuest score, respectively. Heritability of metabolic syndrome components ranged from 0.40 for fasting plasma glucose to 0.61 for body mass index and diabetes mellitus. The heritability for fibrinogen and C-reactive protein was 0.64 and 0.38, respectively. Statistically significant genetic correlations were found between acidity complaints and fasting plasma glucose (ρG = 0.40); sleep disturbances and fasting plasma glucose (ρG = 0.36); acidity complaints and diabetes mellitus (ρG = 0.49) and between total ReQuest score and fasting plasma glucose (ρG = 0.43). The rest of metabolic syndrome components did not correlate with GERD symptoms.ConclusionGenetic factors substantially explain the phenotypic variance of the severity of some GERD symptoms, metabolic syndrome components and inflammation markers. Observed genetic correlations suggest that these phenotypes share common genes. These findings suggest conducting further investigation, as the determination of a linkage analysis in order to identify regions of susceptibility for developing of GERD and metabolic syndrome.

A multifaceted program including strategic planning, organizational culture imprint and care protocols was associated with a significant reduction of adverse events in the respiratory-ICU.

Objective: Identify the association between working conditions, musculoskeletal symptoms and ergonomic demands on nurses. Background:The physical demands of nursing often require repetitive and forced movements that increase the likelihood of developing musculoskeletal disorders, which are the main occupational diseases in this working population.Methodology: Cross-sectional study of 329 nurses chosen at random. Initial symptoms of musculoskeletal disorders (MSDs) were evaluated using Kuorinka's Nordic questionnaire; occupational demands and domestic activities were evaluated using the Individual Survey for Workers' Health, PROESSAT. Logistic regression models were fit to identify associations between musculoskeletal symptoms and occupational activities.Results: A prevalence of 87% and 83% of musculoskeletal disorders was found in the neck and dorsal/lumbar regions, respectively. Using logistic models, associations were identified between ergonomic requirements, exposure time, domestic work, supervision and discomfort in various regions of the body. Conclusions: Postural demands are closely associated with the development of musculoskeletal disorders. Early identification and timely intervention are fundamental. Implications for Nursing Management: Musculoskeletal disorders are very common among nurses and are closely associated with occupational tasks. K E Y W O R D S ergonomic demands, musculoskeletal disorder, nursing, working conditions