Which of the following is the most important determinant of the effectiveness of psychotherapy?

A) the duration of therapy sessions
B) the therapeutic alliance
C) the cost involved in therapy
D) the number of therapy sessions

The therapeutic alliance, which refers to the relationship and level of trust between the therapist and client, has been consistently found to be the most important determinant of the effectiveness of psychotherapy. The duration, cost, and number of therapy sessions can all be important factors as well, but they are not as consistently and significantly related to treatment outcomes as the therapeutic alliance.