The final report is available here: Wikibase Quality Report Final.pdf
Executive Summary Wikibase Quality Report
The quality of the Wikibase source code is generally better than in the average PHP project. Especially the derived projects Ask, DataValues and Diff consist of well crafted code. The most pressing identified issues in the PHP code consist of a too high code complexity of multiple code entities. This leads to a decreased maintainability, because complex code is harder to understand by humans and code pieces cannot easily be replaced. As a result, the implementation of new features and the fixing of errors in the affected code take more time and are more error prone. In addition, implementation of automated tests is harder.