Reliability evaluation of the BIFMA Chair Measurement Device

In the last decade, most offices have been equipped with computers, and most office workers spend much of their time sitting in chairs. And recently, as many office workers complain of back pains, the importance of proper sitting and of chair designs that provide comfortable and suitable sitting posture has become recognized widely.

One organization involved in the design of chairs is the Human Factors and Ergonomics Society (HFES) and its ANSIIHFES 100 committee. This committee has established the ANS/IHFES 100 standard for various types of furniture used at computer workstations, including chairs, desks, and tables. This committee also has designed the Chair Measurement Device (CMD) for specific assessments of seat height, seat depth, seat width, backrest height, backrest width, lumbar support, seat to back included angle, seat pan angle, armrest height, and armrest clearance, for the purpose of developing chairs in connection with other related furniture, such as computer desks. The CMD has been developed through the Business and Institutional Furniture Manufacturer's Association (BIFMA).

The purpose of this study was to evaluate the reliability of the CMD, for future use in evaluating chair design. Eight participants made specific measurements of three chairs over three measurement sessions. Six measurements were taken from each chair: lumbar support height, seat height, seat depth, backrest height, seat pan angle, and seat to back included angle. This experiment produced 2,160 data points, and standard deviation and confidence interval analysis was used to evaluate the inter-evaluator reliability (ie., consistency across the different evaluators) and the intra-evaluator reliability (i.e., consistency within an evaluator).

All standard deviations and 99% confidence intervals of the measurements were very small, implying that the measurements using the CMD were reliable across the evaluators, as well as within evaluators. The results also show that the procedure established for measurements was adequate for ANSIIHFES 100 compliance evaluations.