Abstract

Five experiments were performed to test the hypothesis that the scale-ends shrinkage phenomenon (SSP) in the equal-appearing intervals scale (EIS) is caused by the truncated nature of the scale. In Experiments 1, 2, and 3, Ss judged the 33 attitude statements under one of the 3 conditions (a common, 11-point scale; lower 2 categories omitted; or upper 2 categories omitted) or under two of the conditions. In Experiments 4 (both ends omitted) and 5 (the upper end extended), EIS values were plotted against paired-comparisons scale (PCS) values of 11 statements taken from the initial 33 stimuli. Results showed that truncation increased an SSP, and that adding extra categories to one end of scale resulted in a reduction of SSP in that part of the scale.