Minimum perceived VAS differences at an interval of 7 days

Abstract Aims: To determine the minimum perceived visual analog scale (VAS) difference repeated after 7 days. Methods: An experimental paired design of different controlled pain levels administered by an iontophoretic device. Each study subject received two stimuli, which were separated by a 7 day interval. Subjects were asked to assess their pain levels using a 10 cm VAS and to assess whether the two painful stimuli were different or the same. Results: 40 volunteers were studied. None of the subjects with a VAS difference of 0–0.9 cm could differentiate the difference in pain intensity between the first and the second stimulus. Seven of the nine subjects with a VAS difference of exactly 1.0 cm distinguished the second electrical stimulus as more or less painful than the first electrical stimulus. All 21 subjects with a VAS difference greater than 1.0 cm differentiated the intensity between the first and the second electrical stimuli.