Page 190 - Prevention and Treatment of Incisional Hernia- New Techniques and Materials

Chapter 9
conducted, what was the primary aim or endpoint of the study and how was the endpoint analysed. This knowledge is essential to know whether the results of this study can be extrapolated and generalized to the larger group of patients with the disease treated, so that the study result might in uence the treatment of future patients. Knowledge of the sample procedures used to determine the study population from the screened patients allows the readers to identify potential sources of bias and thus assess the external validity of the study results. Some exemplary hernia-related di erent types of studies: cohort study by Dietz(4), comparative cohort study by Kurian(5), registry study by Helgstrand(6), randomized controlled trial by Bloemen(7), prospective non- randomized clinical trial by Feliu(8), systematic review by Hansson(9) a meta- analysis by Aslani(10).
Study types
All reported studies should have a clear description of the study type, which should be mentioned in the title and/or the abstract of the manuscript. There is a fundamental distinction between observational studies or interventional studies (Figure 1). An outcome variable(s) (aka dependent variable) will be studied in relation to one or more predictor variables (aka independent variables; aka risk factors) in an observational study. Analysis will focus on the association of the predictor(s) with the outcome(s) over a de ned time period. A cohort study is a type observational study in which a group (cohort) is de ned, e.g. all patients undergoing a particular operation or having a certain type of hernia. Most publications on ventral abdominal wall repair are classi ed as non-comparative cohort studies because there is no control group in the study. Rather the results are discussed in relation to other studies published on similar patient populations. In a comparative cohort study or case-control study at least two di erent populations are compared within the study. A registry is a type of cohort study that has a speci c purpose, de ned in advance. The data entered are carefully crafted to answer important questions about the condition or symptom being studied. Results from registry studies are often very informative because such care is taken to assure consistent data de nition, consistent data entry and the enrolment of a large number of patients in relationship to the total a ected population. A cross-sectional study is an observational study, which by de nition is not longitudinal because subjects are studied at a single point in time. An example would be a study investigating the impact of the
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