Most experiments on thermal sensation require the subject to rate his sensation on a numbered scale. The most common is the seven point Bedford scale which consists of 7 points ranging from 1 (much too cool) to 7 (much too warm) • Data are collected from a number of subjects and are then analysed. Although only integral responses are possible from an individual subject 1 responses are treated as real numbers allowing for the use of fractional means when talking about the response of a group.

Research work at the Electricity Council Research Centre has generally used the 7-point rating scale and has found the mean vote of a group on the Bedford scale to be reliable. However an earlier experiment by the author (1) in which 24 subjects returned at an interval of 1 to 3 weeks to experience the same conditions indicated that individual votes are not so reliable. The means of the Bedford votes of the 24 subjects for the 2 identical conditions were 4. 3 and 4. 1 , which are not significantly different. The unsigned difference between an individual's votes on the 2 occasions was used as a measure of reliability I and the mean unsigned difference over all subjects was found to be 1. 1 intervals on the Bedford scale.