 Two years after the project was started, in 2003, a IBM study found that "vandalism is usually repaired extremely quickly—so quickly that most users will never see its effects" and concluded that Wikipedia had "surprisingly effective self-healing capabilities".The inclusion of false or fabricated content has, at times, lasted for years on Wikipedia due to its voluntaristic editorial oversight.Wikipedia has multiple systemic biases due to its editing model, namely selection bias, participation bias, and group-think bias.