Marsh AP, Janssen JA, Ip EH, Barnard RT, Ambrosius WT, Brubaker PR, Burdette JH, Sheedy JL, Rejeski WJ. Assessing Walking Activity in Older Adults: Development and Validation of a Novel Computer-Animated Assessment Tool. J Gerontol A Biol Sci Med Sci. 2015 Dec; 70(12):1555-61.