These limitations of subjective self-report measures and the cost and inconvenience of polysomnography suggest the need for alternative methods of measurement. With the use of an actigraph, a small, highly sensitive, accelerometer (motion detector) worn on the wrist over a period of days, a number of sleep-related variables can be derived through the analysis of motion and rest patterns using a computer algorithm (Coffield & Tryon, 2004). Variables such as sleep latency, total time asleep, and number of nocturnal awakenings derived through actigraphy are comparable to those obtained via polysomnography, and recent research studies demonstrate the validity of actigraph-based sleep/wake estimates among individuals with acquired brain injury (Muller, Czymmek, Thone-Otto, & Von Cramon, 2006; Tweedy & Trost, 2005; Schuiling, Rinkel, Walchenbach, & de Weerd, 2005). Thus, actigraphy represents a means of measurement that will enable the collection of objective data in the comfort of the sleeper's usual environment in a manner that is less invasive and more cost-effective than polysomnography, and more reliable than self-report measures alone.