Complex sentence: Both Freud and Krafft-Ebing were psychiatrists; their observations on sadism and masochism were dependent on psychiatric patients, and their models were built on the assumption of psychopathology.
Split into simpler sentences: Both Freud and Krafft-Ebing were psychiatrists. Their observations on sadism and masochism were dependent on psychiatric patients, and their models were built on the assumption of psychopathology.