The act of measurement is an essential component of scientific research (Streiner & Norman, 2008). Measurement plays an essential role in research in all scientific disciplines; occupational therapy is no exception. In the past few decades, clinical research has become more complex, with the emphasis shifting away from increasing the quantity of life towards an increased awareness of the impact of health care on the quality of human life (Land, Michalos & Sirgy, 2012). Certainly in occupational therapy, therapeutic efforts are directed primarily, albeit not entirely, to the improvement of quality of life, not quantity of life. Therefore to place our profession on a sound scientific foundation, methods must be devised to measure what was previously thought to be unmeasurable and to assess in a reproducible and valid fashion those subjective states (Land et al., 2012).