Scientists critical of parapsychology state that its extraordinary claims demand extraordinary evidence if they are to be taken seriously. Scientists who have evaluated parapsychology have written the entire body of evidence is of poor quality and not adequately controlled. In support of this view, critics cite instances of fraud, flawed studies, and cognitive biases (such as clustering illusion, availability error, confirmation bias, illusion of control, magical thinking, and the bias blind spot) as ways to explain parapsychological results. Research has also shown that people's desire to believe in paranormal phenomena causes them to discount strong evidence that it does not exist.