Statistical analysis
hernia
REGRESSION, SECONDARY, ADVERSE EVENTS
As empirical data for the primary endpoint were not available in the planning stage, the overall rate and treatment effect regarding the primary endpoint were uncertain. Consequently, a sample size calculation was highly uncertain, and thus, the study was performed with an adaptive interim analysis. This design allowed for early stopping of the trial or, if continued, modification of design characteristics—such as recalculation of the sample size—under control of the global type I error rate. The adaptive interim analysis was planned beforehand to take place after the completion of the 12 months follow-up for 80 evaluable patients [Data were described using appropriate measures of location. Due to missing documentation of endpoints and as per initial protocol, patients with missing endpoint documentation on visit 5 (12 months) or more than one occurrence of missing endpoint documentation were documented as missing while patients with at least one endpoint confirmation during the follow-up period (i.e., burst abdomen or incisional hernia) were categorized as positive cases; all others were treated as negative cases. A detailed depiction of this ruling is presented in Additional file The primary endpoint was investigated in a logistic regression model taking into account the group (continuous / interrupted), as well as the covariates BMI (values as measured on the original scale), and age (values as measured on the original scale). For the evaluation of the serious adverse events all available data in the database were considered. Calculations were performed using SAS software (version 9.4; SAS Institute, Inc., Cary, NC, USA). In the case of missing data in secondary endpoints, patients were excluded from statistical analysis of the outcome measure concerned. Due to the explorative nature of the trial all reported p values have to be treated as descriptive statistics without confirmatory value.