How to assess and interpret a prognostic studyPrognosis is the prediction of the evolution of a given disease or event of interest and the frequency of occurrence of specific outcomes. The ideal study design to assess prognosis are cohort studies. However many prognostic studies have case-control or case series designs. Prognostic studies should include all participants with the event of interest of a determinate geographical region, to avoid bias. The measurement precision and exactitude of intervening variables and outcomes, the identification of confounding variables and an adequate follow up period, have a great influence on the methodological quality of prognostic studies. Prognosis is usually expressed as survival, disease free or remission free rates. This article provides basic methodological concepts that should be considered when evaluating a prognostic study.Key words: Prognostic, cohort studies, rates. ResumenPronóstico es una predicción de la evolución de una enfermedad o evento de interés (EI), que se asocia a posibles resultados del EI y a la frecuencia con la cual se puede esperar que se produzcan. El diseño ideal para estudiar pronóstico son los estudios de cohortes, no obstante lo cual, se ha verificado que un importante número de artículos sobre pronóstico corresponden a estudios de casos y controles, y series de casos. Los estudios sobre pronóstico se deben realizar con una población integrada por todas las personas con el EI de una región geográfica definida; es decir, deben basarse en una descripción completa de los individuos estudiados para asegurar una muestra reducida de sesgos. La calidad metodológica de un estudio sobre pronóstico es influenciada por la precisión y exactitud con la que se definen y miden las variables de exposición y resultado; así como por la prolijidad con la que se identifican las potenciales variables de confusión. Involucran un Rev.

Hartmann's procedure and resection with primary anastomosis in diverticular peritonitis Introduction: Colonic diverticulosis, as diverticulitis, is a frequent disease in different stages of evolution. There is uncertainty about treatment options that are used in secondary peritonitis. The aim of this study is to determine the best treatment option for patients with peritonitis secondary to diverticulitis of the left colon in terms of postoperative morbidity (POM) and mortality, comparing Hartmann's procedure (HP) and resection with primary anastomosis (RPA). Material and Methods: Systematic review. Studies in adults with peritonitis secondary to diverticulitis of the left colon treated with HP and RPA published between 1990 and 2011 were analyzed. TRIPDATABSE, IWO, MEDLINE, SciELO and LILACS databases were consulted and search strategies were applied using MeSH and free terms. Selected studies were analyzed using a score of methodological quality (MQ). The following variables were considered: mortality, POM, hospital stay, percentage of bowel transit reconstitution in patients undergoing HP and MQ of primary studies. Results: 26 primary studies were analyzed (47 series). There were no significant differences in the variable mortality (p = 0.0805), but significant difference was observed in POM (incompletely reported) (p = 0.0187). The median of MQ of the studies was 11 points for HP series and 10 for RPA series. Conclusion: The available evidence to determine the best treatment option in terms of mortality and POM in this kind of patients is insufficient. Studies with better level evidence and MQ are needed to clarify the uncertain.