miscarriage of justice can occur when procedures to prevent contamination are not carried out carefully and accurately. Faulty analysis The Innocence Project says 44% of wrongful convictions are the result of faulty forensic analysis. This occurs when forensic experts inadvertently or deliberately misrepresent the significance, validity or reliability of scientific evidence. Over the years, misrepresentations have been made in the arenas of serological analysis, microscopic hair comparison, and the analysis of bite marks, shoe prints, soil, fiber, and fingerprints. Overconfident experts Overly confident testimony by expert witnesses can also lead to miscarriages of justice. The credibility of expert witnesses depends on numerous factors - in particular, their credentials, personal likability and self-confidence which all impact on how believable they are. The confidence with which experts present their evidence has also been noted to influence jurors, who tend to assume that a witness who is anxious or nervous is lying. The manner in which experts testify may have a greater impact on judges and lawyers who prefer experts who provide clear, unequivocal conclusions. The credentials and reputation of the expert also have a significant impact on juries. For example, Charles Smith was head of the Ontario Pediatric Forensic Pathology Unit from 1982 and the most highly regarded specialist in his field. His testimony led to the convictions of thirteen women whose children died in unexplained circumstance before it came to light that he had "a thing against people who hurt children", and "was on a crusade and acted more like a prosecutor" than a pathologist. An inquiry into his conduct concluded in October 2008 that Smith "actively misled" his superiors, "made false and misleading statements" in court and exaggerated his expertise in trials. False confessions The possibility that innocent people would admit to a crime they did not commit seems unlikely - and yet this occurs so often, the Innocence Project found false confessions contribute to approximately 25% of wrongful convictions in murder and rape cases. Certain suspects are more vulnerable to making a false confession under police pressure. This includes individuals who are intellectually impaired, and those who suffer from mental illness. Saul Kassin, a leading expert on false confessions, says that young people are also particularly vulnerable to confessing, especially when stressed, tired, or traumatized. Coercive interrogation techniques Police often use coercive manipulation techniques when conducting interrogations in hopes of obtaining a confession. In the United States, one of