Independent Wheelchair Transfers in the Built Environment: How Transfer Setup Impacts Performance Phase 2: Final Report

Study Limitations

Some limitations that occurred with this study were that occasionally the grab bars would get in the way of a participant transferring to or from the station since they were located on either side of the transfer surface. These participants were observed having to reposition their WMD or having to transfer around the grab bar. A protocol or an option of using only one grab bar or having a removable grab bar may be worth investigating in the future. Also, the grab bars were placed perpendicular to the front edge of the transfer station. This may have forced some participants to approach the station more from the front (e.g. forward-facing) than from the side. However, the study participants on average did not appear to adjust their angle of approach too much in between protocols with and without the grab bars present on the station (Table 14).     
 
Some participants also asked if they could use both size of grab bars on either platform during the two-step transfers. They mentioned that the taller ones were more helpful for going to lower elevations and the lower ones for transferring higher. This was not an option for this study and it may be that developing a grab bar that is angled or easily adjustable in height would be beneficial for future work. There was not a backrest available behind the second platform for the two-step transfers. When performing these transfers to a higher elevation participants could be transferring to a seat around 31.5 inches off the ground. Even though there were spotters standing behind this platform having a wall, backrest, or another step available there would have added to the safety of the transfer. The grab bars attached to this surface did help with keeping the participants stable by allowing another surface to grip onto.

In addition to the grab bars, the backrest can also be seen as a study limitation. In this phase of research, the backrest was placed parallel to the front edge of the first transfer platform whereas in phase 1 the backrest was placed perpendicular to the front edge of the transfer platform.  This phase 2 backrest placement meant that participants were not able to orient themselves right next to the back rest but instead would need to reach across the platform if wanting to use the backrest as a handheld. For many participants, the backrest was too far out of reach for them to grab it which would explain why very few participants placed their hands on the backrest to help them transfer. 

Another limitation concerns the small sample size collected. Although the above sample size analysis suggests that we may have reached a saturation point, for standards research this is still considered a small sample size and may not reflect the demographics of the cohort of individuals who independently transfer. Additional study participants would add to the strength of the study and help to insure the study sample is as representative of the cohort population as possible.

The study was open to children seven years old and older to participate. The Access Board was particularly interested in collecting data from school aged WMD users to provide guidance on playground equipment standards. Extensive efforts were made to advertise the study to different schools, hospitals, and organizations known to work with children and only one family over the course of the study had contacted us to participate.  This family's son was eligible for the study but his parents were not able to bring the child to HERL to be evaluated.  We were able to collect data from young and small adults. The youngest participant was 18 years old and four participants were less than 4.9 feet tall.

Another study limitation was the low ratio of women compared to men in the study (23% of the participants were women). Every effort was made to recruit women into the study and the proportion of women examined in this study is similar to other studies that have involved community dwelling adult wheelchair users [6, 12-14].  There is a lack of data on the numbers of women and men who use WMDs and who independently transfer in the community. Another issue concerning the US census statistic on the numbers of women versus men WMDs is that it does not take into consideration the disparities associated with age and mobility use.  Kaye et al. states that there is a dramatic increase in WMD use with age [15]. Only 0.41% of the general population uses a WMD from the ages of 18 to 64 years, but that percentage increases to 2.99% for the population 65 years or older. It's possible that due to a women's longer life expectancy that the census statistic is skewed towards including more older women (over 65) who would not likely be actively transferring out in the community (e.g. who are residing in institutional settings).  Moreover data on working age adults shows that more men use mobility devices in general than women (1.6% of men vs 1.3% of women of the population) [15].  Our study involved men and women who were mostly working age and thus it’s possible that the true proportion of women to men who actively transfer in the community is closer to that represented in this study.