• r, ELSEVIER International Journal of Industrial Ergonomics 20 (1997) 441 461 InternationalJourn~l of Industrial Ergonomics Validity and reliability of rating scales for seated pressure discomfort Wenqi Shen*, Kenneth C. Parsons Department (?/Human Sciences, Loughborough Universi~ t~[" Technology, Ashby Road, Loughborough, Leicestershire LE11 3TU, UK Received 1 December 1995; revised 30 August 1996 Abstract To investigate seated pressure discomfort requires a valid and reliable technique to measure discomfort. The aims of this study were to test the validity and reliability of several rating scales and select the best for investigation of pressure discomfort. Six scales were tested: a category partitioning scale, the Borg CR-10 scale, the Corlett discomfort scale, an 8-point ordinal scale, a modified intensity and discomfort scale, and a 21-point ratio scale. Twelve subjects took part in the repeated measures test in two sessions, one week apart. A test seating device generated interface pressure from underneath a foam cushion. Four levels of stimulus, 60, 85, 120, and 165 mmHg, were presented to the seated mid-thigh region. Perceived pressure intensity, discomfort level due to the pressure, and overall discomfort were reported using each of the six scales. Reliability was examined by test-retest correlation, relative rating change and coefficient of variations, and validity examined by absoluteness of rating and the functional consistency. Generally, subjects were capable of reporting their sensation of pressure intensity and discomfort by using the rating scale technique. However, the accuracy of rating strongly depended upon the properties of the scale. The category partitioning scale was found to be highly reliable and most valid for rating pressure intensity and perceived discomfort. This scale was also preferred by subjects when compared with the other five scales. Properties of all the six scales were defined and summarised. Relevance to industry The psychometric properties of the six scales provide a basis for industrial engineers and ergonomists in selecting rating instruments for product usability as well as seating comfort. The validated category partitioning scale is very sensitive and accurate. It will find wide application in comfort evaluation and in industrial benchmarking activities. Keywords." Pressure sensation; Psychophysics; Scaling methods; Seating; Subjective judgment 1. Introduction Pressure distribution measurement on the seat- occupant interface is a primary tool for seating * Corresponding author. Tel.: (810) 986-9760; fax: (810) 986-7292; e-mail: wshen@rbiwsl.gmr.com. comfort evaluation (Lee et al., 1990; Zacharkow, 1988; Schneider and Ricci, 1989). If the interface pressure in any region on the interface is excessive for prolonged sitting, it will induce compression discomfort (Hertzberg, 1958, 1972; Chow and Odell, 1978; Drummond et al., 1982; Bader, 1986). Applied research and industrial benchmarking in 0169-8141/97/$17.00 Copyright :.~! 1997 Elsevier Science B.V, All rights reserved PII S01 69-8 1 4 1(96)00068-6