2.3 Analysis
2.3.1 Comparison of Demographic Characteristics of Our Sample and U.S. Population of WhMD Users
The size and functional abilities of WhMD users was hypothesized to differ significantly across gender, device type and age of the individual. A comparative analysis between our sample and the population of U.S. WhMD users provided information about the generalizability of our pooled results with the U.S. population of WhMD users. Demographic information about the U.S. population of WhMD users was obtained through summary reports of the 1994‒95 National Health Interview Survey on Disability (Flagg, 2009; Kaye et al., 2000).
The relative percentages of WhMD users stratified by gender, device type and age categories were compared between our sample and the U.S. population of WhMD users. Cases in which our sample was not considered representative on these variables suggest a “stratified analysis” (i.e. presentation of results for sub-samples, rather than the pooled data set) or other statistical modeling methods (e.g. Paquet et al., in preparation) would provide opportunities for a more valid application of our results to U.S. standards. Population-based data about percentage of WhMDs users with different types of disability were not available for the analyses.
2.3.2 Comparison of Demographic Characteristics of Subsamples by Data Collection Location
Because each of the data collection sites had access to different sub-populations of WhMD users and slightly different methods of participant recruitment, we believed it would be important to understand the differences in the demographic characteristics of the sub-samples of each site.
Therefore the relative percentages of WhMD users stratified by gender, device type and age categories were compared across the study’s three data collection sites.
2.3.3 Comparison of Dimensions with Standards and other Anthropometric Studies
The results of our study were compared to the Americans with Disabilities Act Accessibility Guidelines (ADAAG) and the Americans with Disabilities Act – Architectural Barriers Act Accessibility (ADA-ABA) Guidelines for Buildings and Facilities, standards of several countries and findings from several other large non-U.S. anthropometric studies of WhMD users. To identify the dimensions to compare, we first identified the relevant item in the U.S. standards to identify the common underlying anthropometric variables. Our analysis then focused only on those variables. The list below identifies the items in the standards and the anthropometric variables which were used for comparison:
• Unoccupied Device Width: Compared to the horizontal distance between the most extreme lateral points of the WhMD.
• Unoccupied Device Length: Compared to the horizontal distance between the most extreme posterior and anterior points of the WhMD.
• Clear Floor Space Width: Compared to Occupied Width.
• Clear Floor Space Length: Compared to Occupied Length.
• Seat Height, maximum: Compared to the vertical distance measured from the floor to the height of the seat support surface when occupied.
• Knee Clearance Height, minimum: Compared to the vertical distance measured from the floor to the superior aspect of the right knee.
• Toe Clearance Height, minimum: Compared to the vertical distance measured from the floor to the highest point on the right foot (i.e. higher of either the dorsal or distal foot point). This measure was only considered for manual and power wheelchair users.
• Knee Clearance Depth, minimum: Compared to the horizontal distance measured from the distal aspect of the right knee to the anterior-most point on the occupant and/or wheelchair. This measure was only considered for manual and power wheelchair users.
• Toe Clearance Depth, maximum: Compared to the horizontal distance measured from the dorsal aspect of the foot (i.e. crease of the foot and lower leg) to the anterior-most point on the occupant and/or wheelchair. This measure was only considered for manual and power wheelchair users.
• Wheelchair Turning Space to make a 90-Degree Turn: Compared to the maneuvering clearances required for performing a 90-degree (L-shaped) turn.
• Circular and T-shaped Wheelchair Turning Space: Compared to the maneuvering clearances required to make a 180-degree turn in a space confined on three sides.
• Wheelchair Turning Space to make a 180-Degree Turn around an Obstacle: Compared to the maneuvering clearances required to make a 180-degree turn around a center barrier.
• Circular and T-shaped Wheelchair Turning Space: Compared to the maneuvering clearances required to make a 360-degree turn in a space confined on all four sides.
• Forward Reach Height Lower and Upper Limits: Compared to the measured heights that WhMD user could reach beyond the anterior (forward) most point of the WhMD user or device.
• Side Reach Height Lower and Upper Limits: Compared to the measured heights that WhMD user could reach beyond the most lateral point of the WhMD user or device.
• Side Reach Height Lower and Upper Limits over an obstruction of 610 mm: Compared to the measured heights that WhMD user could reach 610 mm beyond the most lateral point of the WhMD user or device.
• Maximum Forces for Hand-operated Controls: Compared to the maximum hand grip strength in a power grip, and lateral and thumb-forefinger pinch grips.
In order to accomplish the comparative analysis with the standards and other studies, we reviewed ICC/ANSI A117.1 (2003) Accessible and Usable Buildings and Facilities, which serves as the model for the technical requirements in the federal guidelines in the U.S., the Americans with Disabilities Act Accessibility Guidelines (ADAAG) and its eventual replacement, the Americans with Disabilities Act – Architectural Barriers Act Guidelines (ADA-ABA). For the United Kingdom (U.K.), we reviewed BS 8300:2001 Design of Buildings and Their Approaches to Meet the Needs of Disabled People – Code of Practice. For Canada (CA), we reviewed B651‒04 Accessible Design for the Built Environment. For Australia (AUS), we reviewed AS 1428.2 – 1992 Design for Access and Mobility Part 2: Enhanced and Additional Requirements – Buildings and Facilities. Table 2.4 summarizes Accessibility Standards that were used for the comparisons.
Table 2.4 Comparison of Accessibility Standards across Four Countries.
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* This standard also includes an appendix with information on device size and maneuvering spaces for power chairs and scooters derived from the UDI research.
Since the findings of anthropometric research are often voluminous, journal articles and book chapters do not usually include a full documentation. Thus, we obtained the original research reports from Ringaert et al. (2001) from Canada, Stait et al. (2000) from the United Kingdom, Bails (1983) and Seeger et al. (1994) from Australia. The research underlying BS8300:2001 in the U.K. was summarized in an Annex to the standard itself but we were unable to obtain a more comprehensive report that described the details of the methodology. Each of the studies is briefly described below. See Steinfeld et al. (2010c) for a more complete summary of each.
In his study, Bails (1983) recruited participants from attendees at disability support centers and institutions. Eligible participants were between 18 and 60 years of age and used a manual or powered wheelchair. Scooter users were not included in the study. The research focused primarily on testing of full-size simulations of elements found in the built environment, such as doorways, environmental controls, furniture and fixtures that were configured to meet the Australian standards at the time.
Seeger et al. (1994) studied only device size. About 73% of the 240 individuals in the sample lived in nursing homes and other institutions. Forty-five percent were over 65 years old. Eleven percent used power chairs and 2% used scooters. Both unoccupied and occupied dimensions of device width and length were measured as well as a set of other basic dimensions. Measurements were taken manually using conventional measuring tools including a tape measure, steel square and spirit level.
The Department of Environment Transport and the Regions (DETR) (Stait et al., 2000) and the Department for Transport (DfT) (Hitchcock et al., 2006) studies were the two most recent in a series of three large-scale wheelchair anthropometry surveys conducted in the U.K. The studies were limited to the measurement of device size and weight. The DETR survey conducted in 1999, recruited participants solely at an exposition of equipment for people who use wheeled mobility devices for traveling around the community. The subsequent DfT survey was widened to include 12 schools and retail centers in the U.K., in addition to the 2005 Mobility Roadshow. Of the 745 participants in the DETR study whose data was acceptable, 59% used self-propelled manual chairs, 9% used attendant powered chairs, 25% used power chairs and 9% used scooters. Nine percent of the sample were judged to be 16 years of age or younger. The DfT study sample comprised of 1098 adults and 247 children. Among adults, 41% used self-propelled manual chairs, 10% used attendant-propelled wheelchairs, 27% used power chairs, and 22% used scooters. The DETR study used two photographs of each participant, while the DfT study employed seven photographs taken with a camera from pre-determined angles after participants wheeled into position on a scale. A checkerboard pattern on the floor and wall provided references to take measurements off the photographs. Although a wide variety of accessories were observed on the devices, they were not measured as part of the width calculation.
The research used as a basis for revisions to the U.K. BS8300:2001 standards covered clear floor area space requirements, knee clearances and maneuvering clearances. A total of 164 individuals were included in the sample but only 90 participated in the research on space allowances. Due to the lack of a full research report, it is not clear how the measurements were collected and, in many cases, the landmarks used to define them. From the information available, it appears that some scooters and attendant propelled chairs were included in the sample but it is not clear whether these individuals were included in the device or body measurements.
The Universal Design Institute (UDI) study (Ringaert et al., 2001) included a sample of individuals recruited from disability and senior organizations in Winnipeg by written invitation. Of the 50 participants, 35 (70%) used power chairs and 15 (30%) used scooters. The cause of disability for individuals in the sample included a wide range of conditions. Device size and maneuvering spaces were measured. All dimensions were taken to the extremes of the equipment including any object attached to the device like a ventilator. However, the actual landmarks on the devices were not well documented. Measurements were made with rulers and tape measures but no information is given on the accuracy and reliability of these techniques. Maneuvering trials were recorded using overhead video cameras while participants completed standardized movements in simulated environments built with plywood floors and wood framed dividers. Measurements were later taken off the videotapes although the method used to extract the measurements and the reliability of the technique was not described. An observer rating was used to determine successful trials.
The common variables were defined graphically in illustrations and with abbreviations, e.g. Knee Clearance Height (KCH), Knee Clearance Depth – Upper (KCD), and Extended Depth (ED). In many cases, variables underlying the U.S. standards are not included in other standards. Thus, in our comparisons, we omitted values for those variables. We did not, however, report variables from other standards that are not included in the U.S. standards.
The standards did not always use the same variables (or parameters), terminology or measurement conventions. For example, the U.S. standards include both Imperial and “soft” conversions to Metric units, but all the other standards are in Metric units only; there are at least three different terms used for a “wheelchair turning space”, and the U.K. standards report reach ranges for both a “maximum” and “minimum” reach while the U.S. standards have only one range delimited by a minimum and a maximum value.
These differences present several problems to researchers. For example, the definition of a “wheelchair turning space” determines the protocol used to study the clearance needed. Different results are obtained if that space is bounded or unbounded or whether the protocol calls for a smooth continuous turn or includes a series of smaller movements or allows either. Since the standards do not define variables clearly, researchers have made their own interpretations and developed different protocols to study the same variables. Thus, to make comparisons, we standardized all the values from standards and research as much as possible based on a common definition of variables and measurement conventions. We reported the U.S. values in both Imperial and Metric units but did not convert the other countries’ values to Imperial nor did we do “hard” conversions of the Imperial values found in the U.S. standards.
We then reviewed the research completed in each study. In many cases, this required some interpretation because the research studies did not always use the same terms or definitions as the standards in the respective country. Different approaches were also used to report findings. Some results were reported in percentiles. Other results were reported as minimum or maximum values. Still others were reported as the “percentage of subjects accommodated” – those who could perform a task at a certain criterion level.
We devised a graphic method to compare the results of the research studies to each other including our own and to the standards. Most of the studies reported at least a minimum or maximum value and a mean value for each variable studied. These three points were displayed on a graph and coded by study. Where available, percentile data were added to the graph in between the minimum and maximum values and the mean to provide more detail. All the values for each study that represented a distribution were connected by line segments.
For clarity, we pooled data for all mobility devices. However, this can confound comparisons across studies due to differences in the proportion of manual wheelchairs, power chairs, and scooters. Therefore, we also provided tabular data stratified by mobility device type.
2.3.4 Analysis of Door Use Difficulty
The measurement of door use performance was designed as a quasi-experimental study that involved systematically observing and coding WhMD user performance during door use tasks. It therefore required different analysis and comparison approaches.
First, an analysis of the demographic variables for the subset of WhMD users who completed the door use tasks was completed to describe the percentages of men and women, and types of WhMDs used in this sub-group. The mean, median and range of WhMD user age, occupied width, occupied length and maximum power grip were also reported as we thought that these variables might help explain the door use performance among the sub-group.
The level of difficulty experienced for each of the phases of door use was then compared across the three different doors and WhMD types for each of the tasks. Specifically, the percentage of each of the rating scores (minimum effort, moderate effort, maximum effort and impossible) was calculated for each of the three doors and six door use tasks. Those doors and door use tasks having a relatively large percentage of scores exceeding minimum effort were identified as potentially problematic, and a follow-up analysis of these conditions was performed to determine which WhMD user groups had the greatest difficulty with these tasks.
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