Expert testimony on the factors affecting the reliability of eyewitness evidence is allowed in some U.S. jurisdictions, and not in others. In most states, it is left to the discretion of the trial court judge. States generally allowing it include California, Arizona, Colorado, Hawaii, Tennessee (by a 2007 state Supreme Court decision), Ohio, and Kentucky. States generally prohibiting it include Pennsylvania and Missouri. Many states have less clear guidelines under appellate court precedent, such as Mississippi, New York, New Hampshire, and New Jersey. It is often difficult to tell whether expert testimony has been allowed in a given state, since if the trial court lets the expert testify, there is generally no record created. On the other hand, if the expert is not allowed, that becomes a ground of appeal if the defendant is convicted. That means that most cases that generate appellate records are cases only in which the expert was disallowed (and the defendant was convicted).