Keller MB, Yonkers KA, Warshaw MG, Pratt LA, Gollan JK, Massion AO, White K, Swartz AR, Reich J, Lavori PW. Remission and relapse in subjects with panic disorder and panic with agoraphobia: a prospective short-interval naturalistic follow-up. J Nerv Ment Dis. 1994 May; 182(5):290-6.