Title is descriptive and clear. Informs of the type of study and primary outcome Abstract is well written, able to determine research question, results, and conclusions from the abstract. References are complete, recent, and well structures. The references cite important literature for the field.

The introduction provides a well organized and detailed overview of the subject material. Gaps in understanding of the subject material are outlined. The research question is well stated and could fill important gaps in the understanding of the subject material.

The subjects in this study are well defined - the admission records of all adult patients admitted to medicine services at Barnes Jewish Hospital, a major referral hospital in St. Louis Missouri (n = 5507). The only exclusion criteria is that records of patients discharged after death were not included in analysis because they were not at risk of hospital readmission.

The primary endpoint (any cause readmission within 30 days of discharge) is easily measured and is a clear clinical outcome. The statistical methods were appropriate for this type of study, and the study population is representative of any major urban hospital in the USA and likely most of the rest of the world.

These factors give the study a high degree of validity and reliability in this context.

The major weakness of this study is that it is conducted at a single center, which may limit the generalization of this study. The authors acknowledge this weakness in the discussion.

Statistical analysis is discussed in detail, including methods, variables, and software used. Statistical methods are conventional and not controversial. The text presentation of the results is clear and uses appropriate units. Data in tables and figures is clearly and logically presented in a way that helps the reader understand differences between the population that was readmitted in 30 days and the population that was not readmitted within 30 days.

The discussion is well reasoned and based on the information reported in the results section. The authors explain the new data in context of existing knowledge and acknowledge limitations and con founders in the current study.

The conclusions are not overly broad and are based on the information contained in the results and discussion.