In products designed for human variability, the anthropometry (body measurements) of the target user population constitutes a primary source of variability that must be considered in the optimization of the spatial dimensions of the product. Accommodation, which describes the ability of a user to interact with a device or environment in their preferred manner, is a key measure of the performance. Other studies have considered various methods for accounting for the variability in anthropometry in a target user population to calculate estimated accommodation, but few have explicitly considered the effects of secular trends and demographic changes over time on accommodation. This paper considers these changes in the context of a case study involving truck drivers and cab geometry. The truck driver populations are used to illustrate changes in body size and shape over a 30-year period and show how they affect user acceptability of a design. Changes in the percentages of female drivers are also considered, and are shown to have a significant effect on accommodation. The work demonstrates that secular and demographic changes over time significantly affect accommodation, but a well designed product will be more robust to secular changes.
