Most elderly people staving in nursing homes have considerable dementia, and various kinds of recreation program have hence been executed in order to improve or prevent this problem. However the effect of recreation has not been proved quantitatively. In this paper, we show the relationship between actions of elderly people with considerable dementia during recreation and abilities of memorization, emotion control, accommodation to society, etc., and decompose their actions into basic action factors. We propose a design method for recreation programs composed of effective factor actions for improving dementia. We analyze the effect of recreation in an experiment of robot therapy recreation based on the proposed method. © 2008 IEEE.