Abnormal psychology were thought to be possessed by evil spirits that had to be exercised through religious rituals. If exorcism failed, some authorities advocated steps such as confinement, beating, and other types of torture to make the body uninhabitable by witches, demons, and spirits. The belief that witches, demons, and spirits are responsible for the abnormal behavior continued into the 15th century. Swiss alchemist, astrologer, and physician Paracelsus (1493–1541), on the other hand, rejected the idea that abnormal behaviors were caused by witches, demons, and spirits and suggested that people's mind and behaviors were influenced by the movements of the moon and
Abnormal return where: AR - abnormal return for firm i on day t R - actual return for firm i on day t E(R) – expected return for firm i on day t A common practice is to standardise the abnormal returns with the use of the following formula: formula_3 where: SAR - standardised abnormal returns SD – standard deviation of the abnormal returns The SD is calculated with the use of the following formula: formula_4 where: S – the residual variance for firm i, R – the return on the stock market index on day t, R – the average return