For expert testimony to be admissible, the witness must qualify as an expert under Federal Rule of Evidence 702, and the testimony must be helpful to the jury and focus on a subject the average juror knows little about. In addition, the testimony must be relevant and material, it must be reliable or conform with a generally accepted explanatory theory, and its probative value must outweigh any potential prejudicial impact. The reliability test adopted in the case of Frye v. United States is used by some courts and rejected by others. Although the Frye court disallowed polygraph evidence, this evidence has gained limited acceptance in some jurisdictions. Expert witnesses can help in an objection to the introduction of evidence, in overcoming the prosecution's proof of the voluntariness of a defendant's consent to a search, in explaining why a defendant lacked the intent to commit a crime, and in issues related to dog sniff evidence of drugs. In addition, attorneys should use transcripts of experts from other sentencing hearings in support of a lenient sentence, because hearsay is admissible at sentencing. 62 reference notes