Page 191 - Prevention and Treatment of Incisional Hernia- New Techniques and Materials

patients’ BMI on the incidence of incisional hernias in a population of patients with previous laparotomies.
In an interventional study the result of an intervention on a speci c outcome variable is examined. The patient samples compared in the study should ideally only di er in the predictor variable that is in uenced by the intervention. Other variables, called confounders, should be equally distributed between the study groups. Randomization for the predictor variable in a randomized controlled trial (RCT) is the best method to ensure “equality” of the study groups provided the study population is large enough. For this reason RCT’s are assigned a high level of evidence because if the randomisation is performed adequately they have the smallest risk of bias between the study populations. In a comparative non-randomized clinical trial, it is less clear why a speci c patient receives the intervention or not.
In a systematic review, a comprehensive literature research is performed on a speci c topic and a qualitative critical appraisal of the individual studies is performed. Only data from studies that are considered of su cient methodological quality are summarized. In a meta-analysis the quantitative data of the individual studies are pooled and statistically analysed. A meta- analysis of RCT’s is considered the highest level of evidence and thus allows for the highest grade of recommendation. But meta-analyses have considerable limitations to detect di erences as they usually have higher variances than single studies, and thus have limitations to detect di erences with low incidences.
A case report or case series describes an observation or a treatment, which is considered by the authors as rare or novel and thus worthy of publishing in a manuscript.
As shown in gure 1, guidelines are available on the web for speci c types of studies which provide step by step instructions including a check list for authors to assure correct conduct and reporting of their work(11-16). The Cochrane Collaboration at www.cochrane.org summarizes the websites. Many journals only accept manuscripts that conform to these guidelines and require their reviewers and editors to use them when assessing the quality of submissions. Critical appraisal sheets to assess the quality of a study report can be found on the website of the Centre for Evidence Based Medicine from Oxford can be found to(17).
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Recommendations IH research
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