This paper presents statistical analysis of the behaviour of the electrical performance of commercial crystalline silicon photovoltaic (PV) modules tested in the Solar Test Installation of the European Commission's joint Research Centre from 1990 up to 2006 to the IEC Standard 61215 and its direct predecessor CEC Specification 503. A strong correlation between different test results was not observed, indicating that the standard is a set of different, generally independent stress factors. The results confirm the appropriateness of the testing scheme to reveal different module design problems related rather to the production quality control than material weakness in commercial PV modules. (C) 2008 Elsevier B.V. All rights reserved.