Recent developments in psychophysics termed statistical decision theory (or signal detection theory; SDT) and magnitude estimation (ME) are being applied to an increasing variety of previously recalcitrant problems in clinical psychology and medical decision making. One major value of the SDT method lies in the separation of human decision making into a discrimination accuracy measure and a criterion or bias measure. This characteristic is helpful in analyzing confusing situations such as pain assessment, where any number of impressive procedures or manipulations can and do affect the person's willingness to report pain but leave unaffected the detectability of pain-producing stimuli. ME methods as applied to personality research do not limit an individual's assessment of his or her personal reactions (e.g., degree of anxiety or intoxication) to a narrow range of categories devised by the experimenter but allow each person to construct as sensitive and unique a scale as is required. These methods also show superior agreement with psychophysiological measures of such factors. ME and SDT represent a significant advance over current chaotic and unreliable practices in terms of their greater objectivity and precision, parsimonious use of a single language for the laboratory and the clinic, and potential for the quantification of subtle covert psychological behaviors. This review describes applications of SDT and ME to the assessment and understanding of pain, anxiety, psychoactive drugs, and medical decision making.Although scientific progress has been slow technological advance quite rare in psycholin clinical psychology, it has not been for ogy: the discovery and elaboration of general lack of important problems to study. Rather, principles under rigorous laboratory condiweak investigative tools and conceptual con-tions, followed by the gradual application of fusions have hindered advancement. How-these principles to increasingly more complex ever, recent developments in psychophysics, life situations. termed statistical decision theory (SDT; The SDT approach was developed for more sometimes referred to as sensory decision refined measurement of sensory detection and theory or signal detection theory) and mag-recognition, an attempt to correct and surnitude estimation (ME), have shown great mount the well-known deficiencies of the promise and wide applicability to vital human sensory threshold construct (Price, 1966). concerns far removed from simple sensory For example, threshold values differed demetrics. Like behavior modification tech-pending on the particular method of measureniques, these methods represent a kind of me nt used, which precluded comparisons across experiments. Further, the threshold Bridget F. Grant is now at Rutgers University. measure with its major focus on accurate The authors wish to thank Edward Alf, w. A. report neglected much useful and important °f fte manuscript for their information, such as the frequency and patshould be sent to John M. ternin g °f misses and false affirmatives whic...