Polysomnography, the electrophysiological measurement of sleep, is widely used in the clinical setting to diagnose sleep disorders. Using this more objective measure, Masel and colleagues (2001) found a high prevalence of posttraumatic hypersomnia, sleep apnea-hypopnea syndrome and periodic limb movement disorder that was not identified through self-report measures (Masel, Scheibel, Kimbark, & Kuna, 2001). This illustrates the limitations of self-report questionnaires and highlights the need for more objective measures. However, the high cost and inconvenience of polysomnography, requiring multiple electrodes attached to the face, head, and other parts of the body, make it less practical for research studies.