What are the relevant factors for determining whether a statement is involuntary?

at the nature of the interrogation and the circumstances relating to the particular defendant. [Citations.] With respect to the interrogation, among the factors to be considered are ' " 'the crucial element of police coercion [citation]; the length of the interrogation [citation]; its location [citation]; its continuity'. . . .' " [Citation.] With respect to the defendant, the relevant factors are ' " 'the defendant's maturity [citation]; education [citation]; physical condition [citation]; and mental health.' " ' [Citation.] 'A statement is involuntary [citation] when, among other circumstances, it "was ' "extracted by any sort of threats . . . , [or] obtained by any direct or implied promises . . . ." ' " ' [Citation.]" (People v. Dykes (2009) 46 Cal.4th 731, 752 (Dykes).)