What are the factors that determine whether consent to search was voluntary?

3 Although the presence or absence of one of these factors is not dispositive of the voluntariness inquiry in any given case, many of this court's decisions upholding consent as voluntary are supported by at least several of the factors. See, e.g., United States v. Morning, 64 F.3d 531, 533 (9th Cir.1995) (determining that the defendant's consent to search was voluntarily made where the defendant was not under arrest, the police officers did not engage in any coercive behavior, and the defendant signed a written consent form), cert. denied, --- U.S. ----, 116 S.Ct. 1030, 134 L.Ed.2d 108 (1996); United States v. Perez, 37 F.3d 510, 515 (9th Cir.1994) (finding consent to search voluntary in light of the fact that the defendant was not being detained and had signed a written consent form that specifically advised him of his right to refuse consent); United States v. Childs, 944 F.2d 491, 496 (9th Cir.1991) (upholding a search based on voluntary consent when the defendant was advised of his Miranda rights, was told of his right to refuse consent, and signed a written consent form).