The PSE has become the center of much controversy. It was developed to detect levels of significant emotional stress from vocal utterances and was expected to be useful in psychological and psychiatric evaluations and in lie detection. Like the polygraph, the PSE is limited to measuring certain physiological manifestations of psychological stress and requires a means of discriminating between the stress caused by uttering a significant untruth and the stress from any other source. However, significant differences also exist. The PSE processes voice sounds and does not require attached sensors. Responses are evaluated instantaneously and do not involve a wait for chemical reactions. While the polygraph displays raw, unprocessed traces of the heart, breathing, and skin conductivity, the PSE signal-processes the raw input, thus reducing both the training time needed and the subjectivity of the chart reading. In the 10 years of its existence, PSE has faced both the same opposition as the polygraph and the opposition of the polygraph profession itself. Some studies support the PSE's validity, while others deny it. Some validation studies which deny the value of the PSE have not considered the system components as well as the system itself or have been based on attempts to create an artificial model of the real world. However, the PSE was designed specifically for the levels of stress encountered in real-world criminal, security, and clinical applications, and was not intended to accomplish stress measurement of game situations. Most of the studies supporting the PSE have been accomplished by members of the scientific and academic community. Sixty-five footnotes are included.