Recommendations on Standards for the Design of Medical Diagnostic Equipment for Adults with Disabilities, Advisory Committee Final Report

4. Wheelchair seat depth

For this study, wheelchair seat depth was calculated as the horizontal distance from the proximal (i.e., towards the rear) edge to the distal (i.e., towards the forward) edge of the wheelchair seat cushion. Individual wheelchair seat depths are generally about 2 in. less than buttock-popliteal length in most case – this is a rough guideline and is quite similar to deciding seat depths for ambulatory individuals e.g., for office chairs. The median seat depth across different wheeled mobility devices would provide a reference value for the depth of other common seating surfaces. Figure 4 provides a box-plot showing the distribution for wheelchair seat depth stratified by gender and mobility device type.

The median (50th percentile) values for wheelchair seat depth across the 6 sub-groups ranged from 14-17 in. The proposed guidelines recommend a transfer surface depth of 15in. which is at about the middle of this range and may be appropriate.

Figure 4: Box-plot showing the distribution for approximate wheelchair seat depth stratified by gender and mobility device type. The horizontal line splitting the box depicts the median, the box length represents the inter-quartile (25th – 75th percentile) range, and the whiskers represent the minimum and maximum values. Extreme values are shown as dots and asterisks. The red dotted lines depict the observed range of 95th percentile values across sub-groups.