Abstract: An independent survey of investors in European onshore wind was performed. The purpose was to evaluate the skill of the industry at making pre-construction energy yield assessments (EYA’s) and give confidence to the investment community relying on these estimates. Contributors submitted data from 77 projects that have been operating long enough to perform a post-construction energy yield assessment (PCYA). By comparing PCYA’s to EYA’s at these projects observed prediction bias is found. Results show an overall negative bias of 8.9%. Projects are underperforming expectations. Results also show there has been little improvement with time. There were few observable trends in the data that explain why some projects perform better than others although there is a possible connection with wind speed average. Low wind sites appeared more likely to underperform.