A ratio scale for social distance

Choosing a larger-later reward over a smaller-sooner reward may be thought of as altruism toward one's future self. A question that arises in this connection is: What is the relation between delay and social discounting? To begin to answer this question, social and delay discount functions need to be comparable. Delay is ordinarily measured on a ratio scale (time), which allows for meaningful division and addition. Social distance is ordinarily measured on an ordinal scale (rank order of social closeness). To convert social distance to a ratio scale we use a psychophysical distance function obtained via magnitude estimation (Stevens, 1956). The distance functions obtained are well described by a power function (median exponent = 1.9); we show how they may be used to rescale ordinal to ratio social discount functions.