Page 193 - Prevention and Treatment of Incisional Hernia- New Techniques and Materials

Prospective versus retrospective studies
In a prospective study, a cohort of patients is observed for a period of time to look at outcome, e.g. complications, and then relate this to the predictor variables, e.g. type of surgical technique. Interventional studies are prospective studies focused on the outcome of a speci c intervention that is controlled but di erent in the study groups that are compared. A study quali es as prospective if the outcome measurement of the primary endpoint is decided before the start of the study, and the endpoint measurements are performed in the future after the start of the study. Prospective studies are methodologically superior to retrospective studies because the measurements can be controlled and standardized. Moreover the data gathered are usually more homogeneous and complete.
In a retrospective study the investigator looks backwards in time and examines exposure to possible risk or protective factors in relation to an outcome that is established before the start of the study. Thus the study looks at measurements made before the study was started and therefore the data will be less controlled and less homogeneous.
The research question and the primary endpoint
The manuscript of an interventional study should clearly state the research question and/or aim of the study. This research question is translated into a scienti c hypothesis that will be the basis for the study design and the number of patients required to answer the research question. A clinically relevant primary endpoint will be chosen for which the hypothesis is formulated. The primary endpoint or primary variable of a study is the outcome parameter to be measured and compared, either to the control group in a comparative study or to results from the literature in non-comparative studies. For abdominal wall repair, the primary endpoint is most often hernia recurrence, but many other outcome parameters are possible to formulate the hypothesis: acute or chronic pain, Quality of Life, complications, reoperation rates, wound infections, mesh infections, etc. A superiority study investigates if the intervention is superior in comparison to the control group. The results of the study will be compared to the null hypothesis (H0), that there is no di erence between the groups in the primary endpoint measurement. The analysis has to be performed on Intention To Treat (ITT) basis. In ITT analysis, patient outcome is analysed according to the allocated treatment by randomization, regardless wether the patient actually
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Recommendations IH research
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