[Interaction, synergy and antagonism in prospective epidemiological studies]. / Interacción, sinergia y antagonismo en estudios prospectivos en Epidemiología.

In public health there is a growing appreciation for the advantage of the additive scale to better understand the impacts of factors involved in a health event. It is necessary to always remember that the concept of statistical interaction is scale dependent. In the causal relationship between a response and the presence of two or more factors, the concepts interaction, synergy and antagonism are the key ideas. The aim of this note is to show an application of the concepts interaction, synergy and antagonism in prospective studies from a public health perspective. We present three scenarios that illustrate analyses of interaction, independence, synergy and antagonism. Stata 12 software was used for fitting models (log-binomial model and Poisson) and estimating parameters. Appendixes are provided with concepts and Stata commands used in the processes of simulation and parameter estimation.

Interacción, sinergia y antagonismo en estudios prospectivos en Epidemiología / Interaction, synergy and antagonism in prospective Epidemiological studies

En Salud Pública existe una creciente conciencia sobre las ventajas de las escalas aditivas para una mejor comprensión del impacto de los factores involucrados en un evento de salud. Es necesario siempre recordar que el concepto de interacción estadística es escala dependiente. En la relación causal entre una respuesta y la presencia de dos o más factores de exposición los conceptos de interacción, sinergia y antagonismo cobran protagonismo. El objetivo de este documento es mostrar una aplicación de los conceptos interacción, sinergia y antagonismo en estudios prospectivos con una mirada de la salud pública. Se presentan tres situaciones que ilustran dichos conceptos. Se utiliza Stata 12 para el ajuste de modelos (log-binomial y Poisson) y estimación de parámetros. Se aportan anexos con conceptos y comandos de Stata usados en los procesos de simulación y estimación de parámetros.

In public health there is a growing appreciation for the advantage of the additive scale to better understand the impacts of factors involved in a health event. It is necessary to always remember that the concept of statistical interaction is scale dependent. In the causal relationship between a response and the presence of two or more factors, the concepts interaction, synergy and antagonism are the key ideas. The aim of this note is to show an application of the concepts interaction, synergy and antagonism in prospective studies from a public health perspective. We present three scenarios that illustrate analyses of interaction, independence, synergy and antagonism. Stata 12 software was used for fitting models (log-binomial model and Poisson) and estimating parameters. Appendixes are provided with concepts and Stata commands used in the processes of simulation and parameter estimation.

[Post suckling prolactin and estradiol levels as predictors of the time of appearance of the first post partum menstruation]. / ¿Son los niveles de prolactina y estradiol al tercer mes posparto factores predictores del tiempo de aparición de la primera menstruación posparto?: Modelo predictivo mediante análisis de sobrevida.

BACKGROUND: The variability in the duration of lactational amenorrhoea (LA) lead to develop statistical multivariate models to predict the risk of the appearance of the first postpartum menstruation. AIM: To estimate the probability of recovering the first postpartum menstruation by means of a survival analysis, including hormonal levels and other parameters as predictor variables. MATERIAL AND METHODS: Eighty one mothers in exclusive breastfeeding until the sixth postpartum month, in whom estradiol, basal and post suckling prolactin were measured at the third post partum month, were studied. The variables that better predict the appearance of the first menstruation between the 3rd and 12th postpartum months, were identified using a Cox model survival analysis. RESULTS: The median amenorrhea survival time (the lapse when the chance of recovering menstruation is 50%) was 209 days from delivery. Dichotomized estradiol and post suckling prolactin were the only significant variables that predicted the return of menstruation, with cutoff points of 190 pmol/ and 2,550 mIU/L, respectively. CONCLUSIONS: Post suckling prolantin and estradiol levels, measured at the third post partum month, are predictors for the time of appearance of the first postpartum menstruation.

Laparoscopic cholecystectomy: its effect on the prognosis of patients with gallbladder cancer.

Numerous reports suggest more recurrences and a worse prognosis after laparoscopic cholecystectomy (LC) than after open cholecystectomy (OC). The objective of this study was to compare the survival rate of patients undergoing a laparoscopic procedure versus those undergoing an open operation. A series of 24 patients with gallbladder cancer detected after LC were compared with 40 consecutive patients with gallbladder cancer detected after OC. Patients were matched by wall invasion, age, and whether they underwent a reoperation or only cholecystectomy. The series included 2 patients with in situ tumors, 2 with mucosal tumors, 1 with muscular invasion, 13 with subserosal invasion, and 6 with serosal invasion. Recurrences were observed in 4 of the 10 patients with subserosal compromise who underwent reoperation. In contrast, in the OC group of 26 patients with subserosal invasion, 20 of whom were reoperated, only 2 had a recurrence. Of the six patients with serosal infiltration, three in the LC underwent reoperation, all of whom had recurrences that precluded resection. Of the 12 patients in the OC group who presented with serosal invasion, 6 were reoperated and 4 had a recurrence. Overall survival curves did not show differences when patients were compared according to the type of procedure performed. Similarly, the analysis of patients according to the level of wall invasion indicated that there was no significant difference in survival. Although multiple reports have shown a worse prognosis for patients with gallbladder cancer undergoing LC, this study did not show a significant survival difference between the two methods. Although there is a higher but insignificant recurrence rate among the patients who underwent LC, this is not translated into survival.

Evaluación ultrasonográfica del líquido amniótico: medición única del bolsillo vertical mayor / Ultrasonographic assessment of amniotic fluid: single measurement of mayor vertical pocket

En pacientes embarazadas con feto único, edad gestacional conocida y sin factores de riesgo, se les realiza medición única del bolsillo vertical mayor de líquido amniótico por ultrasonografía. Se establece una curva de distribución por percentiles de los promedios de medición del bolsillo vertical mayor de líquido amniótico (mm), a diferentes edades gestacionales (semanas). Los datos fueron analizados a través del Programa Computacional del Sistema de Informática Perinatal (SIP)